diff --git a/README.md b/README.md
index ca5f98f..aec3d49 100644
--- a/README.md
+++ b/README.md
@@ -143,11 +143,10 @@ export class TestPrompt extends PromptElement<PromptProps, PromptState> {
 Please note:
 - If your prompt does asynchronous work e.g. VS Code extension API calls or additional requests to the Copilot API for chunk reranking, you can precompute this state in an optional async `prepare` method. `prepare` is called before `render` and the prepared state will be passed back to your prompt component's sync `render` method.
 - Newlines are not preserved in JSX text or between JSX elements when rendered, and must be explicitly declared with the builtin `<br />` attribute.
-- For now, if two prompt messages _with the same priority_ are up for pruning due to exceeding the token budget, it is not possible for a subtree of the prompt message declared before to prune a subtree of the prompt message declared later.
 
-### Managing your budget
+### Prioritization
 
-If a rendered prompt has more message tokens than can fit into the available context window, the prompt renderer prunes messages with the lowest priority from the `ChatMessage`s result, preserving the order in which they were declared.
+If a rendered prompt has more message tokens than can fit into the available context window, the prompt renderer prunes messages with the lowest priority from the `ChatMessage`s result.
 
 In the above example, each message had the same priority, so they would be pruned in the order in which they were declared, but we could control that by passing a priority to element:
 
@@ -159,9 +158,32 @@ In the above example, each message had the same priority, so they would be prune
 </>
 ```
 
-In this case, a very long `userQuery` would get pruned from the output first if it's too long.
+In this case, a very long `userQuery` would get pruned from the output first if it's too long. Priorities are local in the element tree, so for example the tree of nodes...
+
+```html
+<UserMessage priority={1}>
+  <TextChunk priority={100}>A</TextChunk>
+  <TextChunk priority={0}>B</TextChunk>
+</UserMesssage>
+<SystemMessage priority={2}>
+  <TextChunk priority={200}>C</TextChunk>
+  <TextChunk priority={20}>D</TextChunk>
+</SystemMessage>
+```
+
+...would be pruned in the order `B->A->D->C`. If two sibling elements share the same priority, the renderer looks ahead at their direct children and picks whichever one has a child with the lowest priority: if the `SystemMessage` and `UserMessage` in the above example did not declare priorities, the pruning order would be `B->D->A->C`.
+
+Continuous text strings and elements can both be pruned from the tree. If you have a set of elements that you want to either be include all the time or none of the time, you can use the simple `Chunk` utility element:
+
+```html
+<Chunk>
+  The file I'm editing is: <FileLink file={f}>
+</Chunk>
+```
+
+### Flex Behavior
 
-But, this is not ideal. Instead, we'd prefer to include as much of the query as possible. To do this, we can use the `flexGrow` property, which allows an element to use the remainder of its parent's token budget when it's rendered.
+Wholesale pruning is not always already. Instead, we'd prefer to include as much of the query as possible. To do this, we can use the `flexGrow` property, which allows an element to use the remainder of its parent's token budget when it's rendered.
 
 `prompt-tsx` provides a utility component that supports this use case: `TextChunk`. Given input text, and optionally a delimiting string or regular expression, it'll include as much of the text as possible to fit within its budget:
 
diff --git a/package-lock.json b/package-lock.json
index 20b3ee4..14784c1 100644
--- a/package-lock.json
+++ b/package-lock.json
@@ -14,11 +14,12 @@
 				"@types/vscode": "^1.92.0",
 				"@vscode/test-cli": "^0.0.9",
 				"@vscode/test-electron": "^2.4.1",
+				"cross-env": "^7.0.3",
 				"esbuild": "0.20.2",
 				"mocha": "^10.2.0",
 				"npm-dts": "^1.3.12",
 				"prettier": "^2.8.7",
-				"tsx": "^4.6.2",
+				"tsx": "^4.19.1",
 				"typescript": "^5.6.2"
 			}
 		},
@@ -336,6 +337,22 @@
 				"node": ">=12"
 			}
 		},
+		"node_modules/@esbuild/openbsd-arm64": {
+			"version": "0.23.1",
+			"resolved": "https://registry.npmjs.org/@esbuild/openbsd-arm64/-/openbsd-arm64-0.23.1.tgz",
+			"integrity": "sha512-3x37szhLexNA4bXhLrCC/LImN/YtWis6WXr1VESlfVtVeoFJBRINPJ3f0a/6LV8zpikqoUg4hyXw0sFBt5Cr+Q==",
+			"cpu": [
+				"arm64"
+			],
+			"dev": true,
+			"optional": true,
+			"os": [
+				"openbsd"
+			],
+			"engines": {
+				"node": ">=18"
+			}
+		},
 		"node_modules/@esbuild/openbsd-x64": {
 			"version": "0.20.2",
 			"resolved": "https://registry.npmjs.org/@esbuild/openbsd-x64/-/openbsd-x64-0.20.2.tgz",
@@ -1124,6 +1141,24 @@
 			"integrity": "sha512-ZQBvi1DcpJ4GDqanjucZ2Hj3wEO5pZDS89BWbkcrvdxksJorwUDDZamX9ldFkp9aw2lmBDLgkObEA4DWNJ9FYQ==",
 			"dev": true
 		},
+		"node_modules/cross-env": {
+			"version": "7.0.3",
+			"resolved": "https://registry.npmjs.org/cross-env/-/cross-env-7.0.3.tgz",
+			"integrity": "sha512-+/HKd6EgcQCJGh2PSjZuUitQBQynKor4wrFbRg4DtAgS1aWO+gU52xpH7M9ScGgXSYmAVS9bIJ8EzuaGw0oNAw==",
+			"dev": true,
+			"dependencies": {
+				"cross-spawn": "^7.0.1"
+			},
+			"bin": {
+				"cross-env": "src/bin/cross-env.js",
+				"cross-env-shell": "src/bin/cross-env-shell.js"
+			},
+			"engines": {
+				"node": ">=10.14",
+				"npm": ">=6",
+				"yarn": ">=1"
+			}
+		},
 		"node_modules/cross-spawn": {
 			"version": "7.0.3",
 			"resolved": "https://registry.npmjs.org/cross-spawn/-/cross-spawn-7.0.3.tgz",
@@ -1413,9 +1448,9 @@
 			}
 		},
 		"node_modules/get-tsconfig": {
-			"version": "4.7.3",
-			"resolved": "https://registry.npmjs.org/get-tsconfig/-/get-tsconfig-4.7.3.tgz",
-			"integrity": "sha512-ZvkrzoUA0PQZM6fy6+/Hce561s+faD1rsNwhnO5FelNjyy7EMGJ3Rz1AQ8GYDWjhRs/7dBLOEJvhK8MiEJOAFg==",
+			"version": "4.8.1",
+			"resolved": "https://registry.npmjs.org/get-tsconfig/-/get-tsconfig-4.8.1.tgz",
+			"integrity": "sha512-k9PN+cFBmaLWtVz29SkUoqU5O0slLuHJXt/2P+tMVFT+phsSGXGkp9t3rQIqdz0e+06EHNGs3oM6ZX1s2zHxRg==",
 			"dev": true,
 			"dependencies": {
 				"resolve-pkg-maps": "^1.0.0"
@@ -3078,13 +3113,13 @@
 			}
 		},
 		"node_modules/tsx": {
-			"version": "4.7.1",
-			"resolved": "https://registry.npmjs.org/tsx/-/tsx-4.7.1.tgz",
-			"integrity": "sha512-8d6VuibXHtlN5E3zFkgY8u4DX7Y3Z27zvvPKVmLon/D4AjuKzarkUBTLDBgj9iTQ0hg5xM7c/mYiRVM+HETf0g==",
+			"version": "4.19.1",
+			"resolved": "https://registry.npmjs.org/tsx/-/tsx-4.19.1.tgz",
+			"integrity": "sha512-0flMz1lh74BR4wOvBjuh9olbnwqCPc35OOlfyzHba0Dc+QNUeWX/Gq2YTbnwcWPO3BMd8fkzRVrHcsR+a7z7rA==",
 			"dev": true,
 			"dependencies": {
-				"esbuild": "~0.19.10",
-				"get-tsconfig": "^4.7.2"
+				"esbuild": "~0.23.0",
+				"get-tsconfig": "^4.7.5"
 			},
 			"bin": {
 				"tsx": "dist/cli.mjs"
@@ -3097,9 +3132,9 @@
 			}
 		},
 		"node_modules/tsx/node_modules/@esbuild/aix-ppc64": {
-			"version": "0.19.12",
-			"resolved": "https://registry.npmjs.org/@esbuild/aix-ppc64/-/aix-ppc64-0.19.12.tgz",
-			"integrity": "sha512-bmoCYyWdEL3wDQIVbcyzRyeKLgk2WtWLTWz1ZIAZF/EGbNOwSA6ew3PftJ1PqMiOOGu0OyFMzG53L0zqIpPeNA==",
+			"version": "0.23.1",
+			"resolved": "https://registry.npmjs.org/@esbuild/aix-ppc64/-/aix-ppc64-0.23.1.tgz",
+			"integrity": "sha512-6VhYk1diRqrhBAqpJEdjASR/+WVRtfjpqKuNw11cLiaWpAT/Uu+nokB+UJnevzy/P9C/ty6AOe0dwueMrGh/iQ==",
 			"cpu": [
 				"ppc64"
 			],
@@ -3109,13 +3144,13 @@
 				"aix"
 			],
 			"engines": {
-				"node": ">=12"
+				"node": ">=18"
 			}
 		},
 		"node_modules/tsx/node_modules/@esbuild/android-arm": {
-			"version": "0.19.12",
-			"resolved": "https://registry.npmjs.org/@esbuild/android-arm/-/android-arm-0.19.12.tgz",
-			"integrity": "sha512-qg/Lj1mu3CdQlDEEiWrlC4eaPZ1KztwGJ9B6J+/6G+/4ewxJg7gqj8eVYWvao1bXrqGiW2rsBZFSX3q2lcW05w==",
+			"version": "0.23.1",
+			"resolved": "https://registry.npmjs.org/@esbuild/android-arm/-/android-arm-0.23.1.tgz",
+			"integrity": "sha512-uz6/tEy2IFm9RYOyvKl88zdzZfwEfKZmnX9Cj1BHjeSGNuGLuMD1kR8y5bteYmwqKm1tj8m4cb/aKEorr6fHWQ==",
 			"cpu": [
 				"arm"
 			],
@@ -3125,13 +3160,13 @@
 				"android"
 			],
 			"engines": {
-				"node": ">=12"
+				"node": ">=18"
 			}
 		},
 		"node_modules/tsx/node_modules/@esbuild/android-arm64": {
-			"version": "0.19.12",
-			"resolved": "https://registry.npmjs.org/@esbuild/android-arm64/-/android-arm64-0.19.12.tgz",
-			"integrity": "sha512-P0UVNGIienjZv3f5zq0DP3Nt2IE/3plFzuaS96vihvD0Hd6H/q4WXUGpCxD/E8YrSXfNyRPbpTq+T8ZQioSuPA==",
+			"version": "0.23.1",
+			"resolved": "https://registry.npmjs.org/@esbuild/android-arm64/-/android-arm64-0.23.1.tgz",
+			"integrity": "sha512-xw50ipykXcLstLeWH7WRdQuysJqejuAGPd30vd1i5zSyKK3WE+ijzHmLKxdiCMtH1pHz78rOg0BKSYOSB/2Khw==",
 			"cpu": [
 				"arm64"
 			],
@@ -3141,13 +3176,13 @@
 				"android"
 			],
 			"engines": {
-				"node": ">=12"
+				"node": ">=18"
 			}
 		},
 		"node_modules/tsx/node_modules/@esbuild/android-x64": {
-			"version": "0.19.12",
-			"resolved": "https://registry.npmjs.org/@esbuild/android-x64/-/android-x64-0.19.12.tgz",
-			"integrity": "sha512-3k7ZoUW6Q6YqhdhIaq/WZ7HwBpnFBlW905Fa4s4qWJyiNOgT1dOqDiVAQFwBH7gBRZr17gLrlFCRzF6jFh7Kew==",
+			"version": "0.23.1",
+			"resolved": "https://registry.npmjs.org/@esbuild/android-x64/-/android-x64-0.23.1.tgz",
+			"integrity": "sha512-nlN9B69St9BwUoB+jkyU090bru8L0NA3yFvAd7k8dNsVH8bi9a8cUAUSEcEEgTp2z3dbEDGJGfP6VUnkQnlReg==",
 			"cpu": [
 				"x64"
 			],
@@ -3157,13 +3192,13 @@
 				"android"
 			],
 			"engines": {
-				"node": ">=12"
+				"node": ">=18"
 			}
 		},
 		"node_modules/tsx/node_modules/@esbuild/darwin-arm64": {
-			"version": "0.19.12",
-			"resolved": "https://registry.npmjs.org/@esbuild/darwin-arm64/-/darwin-arm64-0.19.12.tgz",
-			"integrity": "sha512-B6IeSgZgtEzGC42jsI+YYu9Z3HKRxp8ZT3cqhvliEHovq8HSX2YX8lNocDn79gCKJXOSaEot9MVYky7AKjCs8g==",
+			"version": "0.23.1",
+			"resolved": "https://registry.npmjs.org/@esbuild/darwin-arm64/-/darwin-arm64-0.23.1.tgz",
+			"integrity": "sha512-YsS2e3Wtgnw7Wq53XXBLcV6JhRsEq8hkfg91ESVadIrzr9wO6jJDMZnCQbHm1Guc5t/CdDiFSSfWP58FNuvT3Q==",
 			"cpu": [
 				"arm64"
 			],
@@ -3173,13 +3208,13 @@
 				"darwin"
 			],
 			"engines": {
-				"node": ">=12"
+				"node": ">=18"
 			}
 		},
 		"node_modules/tsx/node_modules/@esbuild/darwin-x64": {
-			"version": "0.19.12",
-			"resolved": "https://registry.npmjs.org/@esbuild/darwin-x64/-/darwin-x64-0.19.12.tgz",
-			"integrity": "sha512-hKoVkKzFiToTgn+41qGhsUJXFlIjxI/jSYeZf3ugemDYZldIXIxhvwN6erJGlX4t5h417iFuheZ7l+YVn05N3A==",
+			"version": "0.23.1",
+			"resolved": "https://registry.npmjs.org/@esbuild/darwin-x64/-/darwin-x64-0.23.1.tgz",
+			"integrity": "sha512-aClqdgTDVPSEGgoCS8QDG37Gu8yc9lTHNAQlsztQ6ENetKEO//b8y31MMu2ZaPbn4kVsIABzVLXYLhCGekGDqw==",
 			"cpu": [
 				"x64"
 			],
@@ -3189,13 +3224,13 @@
 				"darwin"
 			],
 			"engines": {
-				"node": ">=12"
+				"node": ">=18"
 			}
 		},
 		"node_modules/tsx/node_modules/@esbuild/freebsd-arm64": {
-			"version": "0.19.12",
-			"resolved": "https://registry.npmjs.org/@esbuild/freebsd-arm64/-/freebsd-arm64-0.19.12.tgz",
-			"integrity": "sha512-4aRvFIXmwAcDBw9AueDQ2YnGmz5L6obe5kmPT8Vd+/+x/JMVKCgdcRwH6APrbpNXsPz+K653Qg8HB/oXvXVukA==",
+			"version": "0.23.1",
+			"resolved": "https://registry.npmjs.org/@esbuild/freebsd-arm64/-/freebsd-arm64-0.23.1.tgz",
+			"integrity": "sha512-h1k6yS8/pN/NHlMl5+v4XPfikhJulk4G+tKGFIOwURBSFzE8bixw1ebjluLOjfwtLqY0kewfjLSrO6tN2MgIhA==",
 			"cpu": [
 				"arm64"
 			],
@@ -3205,13 +3240,13 @@
 				"freebsd"
 			],
 			"engines": {
-				"node": ">=12"
+				"node": ">=18"
 			}
 		},
 		"node_modules/tsx/node_modules/@esbuild/freebsd-x64": {
-			"version": "0.19.12",
-			"resolved": "https://registry.npmjs.org/@esbuild/freebsd-x64/-/freebsd-x64-0.19.12.tgz",
-			"integrity": "sha512-EYoXZ4d8xtBoVN7CEwWY2IN4ho76xjYXqSXMNccFSx2lgqOG/1TBPW0yPx1bJZk94qu3tX0fycJeeQsKovA8gg==",
+			"version": "0.23.1",
+			"resolved": "https://registry.npmjs.org/@esbuild/freebsd-x64/-/freebsd-x64-0.23.1.tgz",
+			"integrity": "sha512-lK1eJeyk1ZX8UklqFd/3A60UuZ/6UVfGT2LuGo3Wp4/z7eRTRYY+0xOu2kpClP+vMTi9wKOfXi2vjUpO1Ro76g==",
 			"cpu": [
 				"x64"
 			],
@@ -3221,13 +3256,13 @@
 				"freebsd"
 			],
 			"engines": {
-				"node": ">=12"
+				"node": ">=18"
 			}
 		},
 		"node_modules/tsx/node_modules/@esbuild/linux-arm": {
-			"version": "0.19.12",
-			"resolved": "https://registry.npmjs.org/@esbuild/linux-arm/-/linux-arm-0.19.12.tgz",
-			"integrity": "sha512-J5jPms//KhSNv+LO1S1TX1UWp1ucM6N6XuL6ITdKWElCu8wXP72l9MM0zDTzzeikVyqFE6U8YAV9/tFyj0ti+w==",
+			"version": "0.23.1",
+			"resolved": "https://registry.npmjs.org/@esbuild/linux-arm/-/linux-arm-0.23.1.tgz",
+			"integrity": "sha512-CXXkzgn+dXAPs3WBwE+Kvnrf4WECwBdfjfeYHpMeVxWE0EceB6vhWGShs6wi0IYEqMSIzdOF1XjQ/Mkm5d7ZdQ==",
 			"cpu": [
 				"arm"
 			],
@@ -3237,13 +3272,13 @@
 				"linux"
 			],
 			"engines": {
-				"node": ">=12"
+				"node": ">=18"
 			}
 		},
 		"node_modules/tsx/node_modules/@esbuild/linux-arm64": {
-			"version": "0.19.12",
-			"resolved": "https://registry.npmjs.org/@esbuild/linux-arm64/-/linux-arm64-0.19.12.tgz",
-			"integrity": "sha512-EoTjyYyLuVPfdPLsGVVVC8a0p1BFFvtpQDB/YLEhaXyf/5bczaGeN15QkR+O4S5LeJ92Tqotve7i1jn35qwvdA==",
+			"version": "0.23.1",
+			"resolved": "https://registry.npmjs.org/@esbuild/linux-arm64/-/linux-arm64-0.23.1.tgz",
+			"integrity": "sha512-/93bf2yxencYDnItMYV/v116zff6UyTjo4EtEQjUBeGiVpMmffDNUyD9UN2zV+V3LRV3/on4xdZ26NKzn6754g==",
 			"cpu": [
 				"arm64"
 			],
@@ -3253,13 +3288,13 @@
 				"linux"
 			],
 			"engines": {
-				"node": ">=12"
+				"node": ">=18"
 			}
 		},
 		"node_modules/tsx/node_modules/@esbuild/linux-ia32": {
-			"version": "0.19.12",
-			"resolved": "https://registry.npmjs.org/@esbuild/linux-ia32/-/linux-ia32-0.19.12.tgz",
-			"integrity": "sha512-Thsa42rrP1+UIGaWz47uydHSBOgTUnwBwNq59khgIwktK6x60Hivfbux9iNR0eHCHzOLjLMLfUMLCypBkZXMHA==",
+			"version": "0.23.1",
+			"resolved": "https://registry.npmjs.org/@esbuild/linux-ia32/-/linux-ia32-0.23.1.tgz",
+			"integrity": "sha512-VTN4EuOHwXEkXzX5nTvVY4s7E/Krz7COC8xkftbbKRYAl96vPiUssGkeMELQMOnLOJ8k3BY1+ZY52tttZnHcXQ==",
 			"cpu": [
 				"ia32"
 			],
@@ -3269,13 +3304,13 @@
 				"linux"
 			],
 			"engines": {
-				"node": ">=12"
+				"node": ">=18"
 			}
 		},
 		"node_modules/tsx/node_modules/@esbuild/linux-loong64": {
-			"version": "0.19.12",
-			"resolved": "https://registry.npmjs.org/@esbuild/linux-loong64/-/linux-loong64-0.19.12.tgz",
-			"integrity": "sha512-LiXdXA0s3IqRRjm6rV6XaWATScKAXjI4R4LoDlvO7+yQqFdlr1Bax62sRwkVvRIrwXxvtYEHHI4dm50jAXkuAA==",
+			"version": "0.23.1",
+			"resolved": "https://registry.npmjs.org/@esbuild/linux-loong64/-/linux-loong64-0.23.1.tgz",
+			"integrity": "sha512-Vx09LzEoBa5zDnieH8LSMRToj7ir/Jeq0Gu6qJ/1GcBq9GkfoEAoXvLiW1U9J1qE/Y/Oyaq33w5p2ZWrNNHNEw==",
 			"cpu": [
 				"loong64"
 			],
@@ -3285,13 +3320,13 @@
 				"linux"
 			],
 			"engines": {
-				"node": ">=12"
+				"node": ">=18"
 			}
 		},
 		"node_modules/tsx/node_modules/@esbuild/linux-mips64el": {
-			"version": "0.19.12",
-			"resolved": "https://registry.npmjs.org/@esbuild/linux-mips64el/-/linux-mips64el-0.19.12.tgz",
-			"integrity": "sha512-fEnAuj5VGTanfJ07ff0gOA6IPsvrVHLVb6Lyd1g2/ed67oU1eFzL0r9WL7ZzscD+/N6i3dWumGE1Un4f7Amf+w==",
+			"version": "0.23.1",
+			"resolved": "https://registry.npmjs.org/@esbuild/linux-mips64el/-/linux-mips64el-0.23.1.tgz",
+			"integrity": "sha512-nrFzzMQ7W4WRLNUOU5dlWAqa6yVeI0P78WKGUo7lg2HShq/yx+UYkeNSE0SSfSure0SqgnsxPvmAUu/vu0E+3Q==",
 			"cpu": [
 				"mips64el"
 			],
@@ -3301,13 +3336,13 @@
 				"linux"
 			],
 			"engines": {
-				"node": ">=12"
+				"node": ">=18"
 			}
 		},
 		"node_modules/tsx/node_modules/@esbuild/linux-ppc64": {
-			"version": "0.19.12",
-			"resolved": "https://registry.npmjs.org/@esbuild/linux-ppc64/-/linux-ppc64-0.19.12.tgz",
-			"integrity": "sha512-nYJA2/QPimDQOh1rKWedNOe3Gfc8PabU7HT3iXWtNUbRzXS9+vgB0Fjaqr//XNbd82mCxHzik2qotuI89cfixg==",
+			"version": "0.23.1",
+			"resolved": "https://registry.npmjs.org/@esbuild/linux-ppc64/-/linux-ppc64-0.23.1.tgz",
+			"integrity": "sha512-dKN8fgVqd0vUIjxuJI6P/9SSSe/mB9rvA98CSH2sJnlZ/OCZWO1DJvxj8jvKTfYUdGfcq2dDxoKaC6bHuTlgcw==",
 			"cpu": [
 				"ppc64"
 			],
@@ -3317,13 +3352,13 @@
 				"linux"
 			],
 			"engines": {
-				"node": ">=12"
+				"node": ">=18"
 			}
 		},
 		"node_modules/tsx/node_modules/@esbuild/linux-riscv64": {
-			"version": "0.19.12",
-			"resolved": "https://registry.npmjs.org/@esbuild/linux-riscv64/-/linux-riscv64-0.19.12.tgz",
-			"integrity": "sha512-2MueBrlPQCw5dVJJpQdUYgeqIzDQgw3QtiAHUC4RBz9FXPrskyyU3VI1hw7C0BSKB9OduwSJ79FTCqtGMWqJHg==",
+			"version": "0.23.1",
+			"resolved": "https://registry.npmjs.org/@esbuild/linux-riscv64/-/linux-riscv64-0.23.1.tgz",
+			"integrity": "sha512-5AV4Pzp80fhHL83JM6LoA6pTQVWgB1HovMBsLQ9OZWLDqVY8MVobBXNSmAJi//Csh6tcY7e7Lny2Hg1tElMjIA==",
 			"cpu": [
 				"riscv64"
 			],
@@ -3333,13 +3368,13 @@
 				"linux"
 			],
 			"engines": {
-				"node": ">=12"
+				"node": ">=18"
 			}
 		},
 		"node_modules/tsx/node_modules/@esbuild/linux-s390x": {
-			"version": "0.19.12",
-			"resolved": "https://registry.npmjs.org/@esbuild/linux-s390x/-/linux-s390x-0.19.12.tgz",
-			"integrity": "sha512-+Pil1Nv3Umes4m3AZKqA2anfhJiVmNCYkPchwFJNEJN5QxmTs1uzyy4TvmDrCRNT2ApwSari7ZIgrPeUx4UZDg==",
+			"version": "0.23.1",
+			"resolved": "https://registry.npmjs.org/@esbuild/linux-s390x/-/linux-s390x-0.23.1.tgz",
+			"integrity": "sha512-9ygs73tuFCe6f6m/Tb+9LtYxWR4c9yg7zjt2cYkjDbDpV/xVn+68cQxMXCjUpYwEkze2RcU/rMnfIXNRFmSoDw==",
 			"cpu": [
 				"s390x"
 			],
@@ -3349,13 +3384,13 @@
 				"linux"
 			],
 			"engines": {
-				"node": ">=12"
+				"node": ">=18"
 			}
 		},
 		"node_modules/tsx/node_modules/@esbuild/linux-x64": {
-			"version": "0.19.12",
-			"resolved": "https://registry.npmjs.org/@esbuild/linux-x64/-/linux-x64-0.19.12.tgz",
-			"integrity": "sha512-B71g1QpxfwBvNrfyJdVDexenDIt1CiDN1TIXLbhOw0KhJzE78KIFGX6OJ9MrtC0oOqMWf+0xop4qEU8JrJTwCg==",
+			"version": "0.23.1",
+			"resolved": "https://registry.npmjs.org/@esbuild/linux-x64/-/linux-x64-0.23.1.tgz",
+			"integrity": "sha512-EV6+ovTsEXCPAp58g2dD68LxoP/wK5pRvgy0J/HxPGB009omFPv3Yet0HiaqvrIrgPTBuC6wCH1LTOY91EO5hQ==",
 			"cpu": [
 				"x64"
 			],
@@ -3365,13 +3400,13 @@
 				"linux"
 			],
 			"engines": {
-				"node": ">=12"
+				"node": ">=18"
 			}
 		},
 		"node_modules/tsx/node_modules/@esbuild/netbsd-x64": {
-			"version": "0.19.12",
-			"resolved": "https://registry.npmjs.org/@esbuild/netbsd-x64/-/netbsd-x64-0.19.12.tgz",
-			"integrity": "sha512-3ltjQ7n1owJgFbuC61Oj++XhtzmymoCihNFgT84UAmJnxJfm4sYCiSLTXZtE00VWYpPMYc+ZQmB6xbSdVh0JWA==",
+			"version": "0.23.1",
+			"resolved": "https://registry.npmjs.org/@esbuild/netbsd-x64/-/netbsd-x64-0.23.1.tgz",
+			"integrity": "sha512-aevEkCNu7KlPRpYLjwmdcuNz6bDFiE7Z8XC4CPqExjTvrHugh28QzUXVOZtiYghciKUacNktqxdpymplil1beA==",
 			"cpu": [
 				"x64"
 			],
@@ -3381,13 +3416,13 @@
 				"netbsd"
 			],
 			"engines": {
-				"node": ">=12"
+				"node": ">=18"
 			}
 		},
 		"node_modules/tsx/node_modules/@esbuild/openbsd-x64": {
-			"version": "0.19.12",
-			"resolved": "https://registry.npmjs.org/@esbuild/openbsd-x64/-/openbsd-x64-0.19.12.tgz",
-			"integrity": "sha512-RbrfTB9SWsr0kWmb9srfF+L933uMDdu9BIzdA7os2t0TXhCRjrQyCeOt6wVxr79CKD4c+p+YhCj31HBkYcXebw==",
+			"version": "0.23.1",
+			"resolved": "https://registry.npmjs.org/@esbuild/openbsd-x64/-/openbsd-x64-0.23.1.tgz",
+			"integrity": "sha512-aY2gMmKmPhxfU+0EdnN+XNtGbjfQgwZj43k8G3fyrDM/UdZww6xrWxmDkuz2eCZchqVeABjV5BpildOrUbBTqA==",
 			"cpu": [
 				"x64"
 			],
@@ -3397,13 +3432,13 @@
 				"openbsd"
 			],
 			"engines": {
-				"node": ">=12"
+				"node": ">=18"
 			}
 		},
 		"node_modules/tsx/node_modules/@esbuild/sunos-x64": {
-			"version": "0.19.12",
-			"resolved": "https://registry.npmjs.org/@esbuild/sunos-x64/-/sunos-x64-0.19.12.tgz",
-			"integrity": "sha512-HKjJwRrW8uWtCQnQOz9qcU3mUZhTUQvi56Q8DPTLLB+DawoiQdjsYq+j+D3s9I8VFtDr+F9CjgXKKC4ss89IeA==",
+			"version": "0.23.1",
+			"resolved": "https://registry.npmjs.org/@esbuild/sunos-x64/-/sunos-x64-0.23.1.tgz",
+			"integrity": "sha512-RBRT2gqEl0IKQABT4XTj78tpk9v7ehp+mazn2HbUeZl1YMdaGAQqhapjGTCe7uw7y0frDi4gS0uHzhvpFuI1sA==",
 			"cpu": [
 				"x64"
 			],
@@ -3413,13 +3448,13 @@
 				"sunos"
 			],
 			"engines": {
-				"node": ">=12"
+				"node": ">=18"
 			}
 		},
 		"node_modules/tsx/node_modules/@esbuild/win32-arm64": {
-			"version": "0.19.12",
-			"resolved": "https://registry.npmjs.org/@esbuild/win32-arm64/-/win32-arm64-0.19.12.tgz",
-			"integrity": "sha512-URgtR1dJnmGvX864pn1B2YUYNzjmXkuJOIqG2HdU62MVS4EHpU2946OZoTMnRUHklGtJdJZ33QfzdjGACXhn1A==",
+			"version": "0.23.1",
+			"resolved": "https://registry.npmjs.org/@esbuild/win32-arm64/-/win32-arm64-0.23.1.tgz",
+			"integrity": "sha512-4O+gPR5rEBe2FpKOVyiJ7wNDPA8nGzDuJ6gN4okSA1gEOYZ67N8JPk58tkWtdtPeLz7lBnY6I5L3jdsr3S+A6A==",
 			"cpu": [
 				"arm64"
 			],
@@ -3429,13 +3464,13 @@
 				"win32"
 			],
 			"engines": {
-				"node": ">=12"
+				"node": ">=18"
 			}
 		},
 		"node_modules/tsx/node_modules/@esbuild/win32-ia32": {
-			"version": "0.19.12",
-			"resolved": "https://registry.npmjs.org/@esbuild/win32-ia32/-/win32-ia32-0.19.12.tgz",
-			"integrity": "sha512-+ZOE6pUkMOJfmxmBZElNOx72NKpIa/HFOMGzu8fqzQJ5kgf6aTGrcJaFsNiVMH4JKpMipyK+7k0n2UXN7a8YKQ==",
+			"version": "0.23.1",
+			"resolved": "https://registry.npmjs.org/@esbuild/win32-ia32/-/win32-ia32-0.23.1.tgz",
+			"integrity": "sha512-BcaL0Vn6QwCwre3Y717nVHZbAa4UBEigzFm6VdsVdT/MbZ38xoj1X9HPkZhbmaBGUD1W8vxAfffbDe8bA6AKnQ==",
 			"cpu": [
 				"ia32"
 			],
@@ -3445,13 +3480,13 @@
 				"win32"
 			],
 			"engines": {
-				"node": ">=12"
+				"node": ">=18"
 			}
 		},
 		"node_modules/tsx/node_modules/@esbuild/win32-x64": {
-			"version": "0.19.12",
-			"resolved": "https://registry.npmjs.org/@esbuild/win32-x64/-/win32-x64-0.19.12.tgz",
-			"integrity": "sha512-T1QyPSDCyMXaO3pzBkF96E8xMkiRYbUEZADd29SyPGabqxMViNoii+NcK7eWJAEoU6RZyEm5lVSIjTmcdoB9HA==",
+			"version": "0.23.1",
+			"resolved": "https://registry.npmjs.org/@esbuild/win32-x64/-/win32-x64-0.23.1.tgz",
+			"integrity": "sha512-BHpFFeslkWrXWyUPnbKm+xYYVYruCinGcftSBaa8zoF9hZO4BcSCFUvHVTtzpIY6YzUnYtuEhZ+C9iEXjxnasg==",
 			"cpu": [
 				"x64"
 			],
@@ -3461,45 +3496,46 @@
 				"win32"
 			],
 			"engines": {
-				"node": ">=12"
+				"node": ">=18"
 			}
 		},
 		"node_modules/tsx/node_modules/esbuild": {
-			"version": "0.19.12",
-			"resolved": "https://registry.npmjs.org/esbuild/-/esbuild-0.19.12.tgz",
-			"integrity": "sha512-aARqgq8roFBj054KvQr5f1sFu0D65G+miZRCuJyJ0G13Zwx7vRar5Zhn2tkQNzIXcBrNVsv/8stehpj+GAjgbg==",
+			"version": "0.23.1",
+			"resolved": "https://registry.npmjs.org/esbuild/-/esbuild-0.23.1.tgz",
+			"integrity": "sha512-VVNz/9Sa0bs5SELtn3f7qhJCDPCF5oMEl5cO9/SSinpE9hbPVvxbd572HH5AKiP7WD8INO53GgfDDhRjkylHEg==",
 			"dev": true,
 			"hasInstallScript": true,
 			"bin": {
 				"esbuild": "bin/esbuild"
 			},
 			"engines": {
-				"node": ">=12"
+				"node": ">=18"
 			},
 			"optionalDependencies": {
-				"@esbuild/aix-ppc64": "0.19.12",
-				"@esbuild/android-arm": "0.19.12",
-				"@esbuild/android-arm64": "0.19.12",
-				"@esbuild/android-x64": "0.19.12",
-				"@esbuild/darwin-arm64": "0.19.12",
-				"@esbuild/darwin-x64": "0.19.12",
-				"@esbuild/freebsd-arm64": "0.19.12",
-				"@esbuild/freebsd-x64": "0.19.12",
-				"@esbuild/linux-arm": "0.19.12",
-				"@esbuild/linux-arm64": "0.19.12",
-				"@esbuild/linux-ia32": "0.19.12",
-				"@esbuild/linux-loong64": "0.19.12",
-				"@esbuild/linux-mips64el": "0.19.12",
-				"@esbuild/linux-ppc64": "0.19.12",
-				"@esbuild/linux-riscv64": "0.19.12",
-				"@esbuild/linux-s390x": "0.19.12",
-				"@esbuild/linux-x64": "0.19.12",
-				"@esbuild/netbsd-x64": "0.19.12",
-				"@esbuild/openbsd-x64": "0.19.12",
-				"@esbuild/sunos-x64": "0.19.12",
-				"@esbuild/win32-arm64": "0.19.12",
-				"@esbuild/win32-ia32": "0.19.12",
-				"@esbuild/win32-x64": "0.19.12"
+				"@esbuild/aix-ppc64": "0.23.1",
+				"@esbuild/android-arm": "0.23.1",
+				"@esbuild/android-arm64": "0.23.1",
+				"@esbuild/android-x64": "0.23.1",
+				"@esbuild/darwin-arm64": "0.23.1",
+				"@esbuild/darwin-x64": "0.23.1",
+				"@esbuild/freebsd-arm64": "0.23.1",
+				"@esbuild/freebsd-x64": "0.23.1",
+				"@esbuild/linux-arm": "0.23.1",
+				"@esbuild/linux-arm64": "0.23.1",
+				"@esbuild/linux-ia32": "0.23.1",
+				"@esbuild/linux-loong64": "0.23.1",
+				"@esbuild/linux-mips64el": "0.23.1",
+				"@esbuild/linux-ppc64": "0.23.1",
+				"@esbuild/linux-riscv64": "0.23.1",
+				"@esbuild/linux-s390x": "0.23.1",
+				"@esbuild/linux-x64": "0.23.1",
+				"@esbuild/netbsd-x64": "0.23.1",
+				"@esbuild/openbsd-arm64": "0.23.1",
+				"@esbuild/openbsd-x64": "0.23.1",
+				"@esbuild/sunos-x64": "0.23.1",
+				"@esbuild/win32-arm64": "0.23.1",
+				"@esbuild/win32-ia32": "0.23.1",
+				"@esbuild/win32-x64": "0.23.1"
 			}
 		},
 		"node_modules/typescript": {
diff --git a/package.json b/package.json
index 1a5e039..71e385d 100644
--- a/package.json
+++ b/package.json
@@ -1,6 +1,6 @@
 {
 	"name": "@vscode/prompt-tsx",
-	"version": "0.2.11-alpha",
+	"version": "0.3.0-alpha.1",
 	"description": "Declare LLM prompts with TSX",
 	"main": "./dist/base/index.js",
 	"types": "./dist/base/index.d.ts",
@@ -9,6 +9,7 @@
 		"compile": "tsc -p tsconfig.json && tsx ./build/postcompile.ts",
 		"watch": "tsc --watch --sourceMap",
 		"test": "vscode-test",
+		"test:unit": "cross-env IS_OUTSIDE_VSCODE=1 mocha --import=tsx -u tdd \"src/base/test/**/*.test.{ts,tsx}\"",
 		"prettier": "prettier --list-different --write --cache .",
 		"prepare": "tsx ./build/postinstall.ts"
 	},
@@ -21,14 +22,15 @@
 	"devDependencies": {
 		"@microsoft/tiktokenizer": "^1.0.6",
 		"@types/node": "^20.11.30",
+		"@types/vscode": "^1.92.0",
 		"@vscode/test-cli": "^0.0.9",
 		"@vscode/test-electron": "^2.4.1",
-		"@types/vscode": "^1.92.0",
+		"cross-env": "^7.0.3",
 		"esbuild": "0.20.2",
 		"mocha": "^10.2.0",
 		"npm-dts": "^1.3.12",
 		"prettier": "^2.8.7",
-		"tsx": "^4.6.2",
+		"tsx": "^4.19.1",
 		"typescript": "^5.6.2"
 	}
 }
diff --git a/src/base/index.ts b/src/base/index.ts
index aa8c76d..6351417 100644
--- a/src/base/index.ts
+++ b/src/base/index.ts
@@ -20,7 +20,7 @@ export * from './tracer';
 export * from './tsx-globals';
 export * from './types';
 
-export { AssistantMessage, FunctionMessage, PrioritizedList, PrioritizedListProps, SystemMessage, TextChunk, TextChunkProps, UserMessage } from './promptElements';
+export { AssistantMessage, FunctionMessage, PrioritizedList, PrioritizedListProps, SystemMessage, TextChunk, TextChunkProps, UserMessage, LegacyPrioritization, Chunk } from './promptElements';
 
 export { PromptElement } from './promptElement';
 export { MetadataMap, PromptRenderer, QueueItem, RenderPromptResult } from './promptRenderer';
@@ -82,15 +82,14 @@ export async function renderPrompt<P extends BasePromptElementProps>(
 		? new AnyTokenizer((text, token) => tokenizerMetadata.countTokens(text, token))
 		: tokenizerMetadata;
 	const renderer = new PromptRenderer(endpoint, ctor, props, tokenizer);
-	let { messages, tokenCount, references } = await renderer.render(progress, token);
-	const metadatas = renderer.getAllMeta();
+	let { messages, tokenCount, references, metadata } = await renderer.render(progress, token);
 	const usedContext = renderer.getUsedContext();
 
 	if (mode === 'vscode') {
 		messages = toVsCodeChatMessages(messages);
 	}
 
-	return { messages, tokenCount, metadatas, usedContext, references };
+	return { messages, tokenCount, metadatas: metadata, usedContext, references };
 }
 
 /**
diff --git a/src/base/jsonTypes.ts b/src/base/jsonTypes.ts
index 7fbfe73..dea3ad0 100644
--- a/src/base/jsonTypes.ts
+++ b/src/base/jsonTypes.ts
@@ -19,13 +19,6 @@ import { UriComponents } from './util/vs/common/uri';
 export const enum PromptNodeType {
 	Piece = 1,
 	Text = 2,
-	LineBreak = 3
-}
-
-export interface LineBreakJSON {
-	type: PromptNodeType.LineBreak;
-	isExplicit: boolean;
-	priority: number | undefined;
 }
 
 export interface TextJSON {
@@ -33,6 +26,7 @@ export interface TextJSON {
 	text: string;
 	priority: number | undefined;
 	references: PromptReferenceJSON[] | undefined;
+	lineBreakBefore: boolean | undefined;
 }
 
 /**
@@ -55,7 +49,7 @@ export interface PieceJSON {
 	props?: Record<string, unknown>;
 }
 
-export type PromptNodeJSON = PieceJSON | TextJSON | LineBreakJSON;
+export type PromptNodeJSON = PieceJSON | TextJSON;
 
 export type UriOrLocationJSON = UriComponents | { uri: UriComponents, range: Range };
 
diff --git a/src/base/materialized.ts b/src/base/materialized.ts
new file mode 100644
index 0000000..7cfe4ec
--- /dev/null
+++ b/src/base/materialized.ts
@@ -0,0 +1,372 @@
+/*---------------------------------------------------------------------------------------------
+ *  Copyright (c) Microsoft Corporation and GitHub. All rights reserved.
+ *--------------------------------------------------------------------------------------------*/
+
+import { once } from './once';
+import { ChatMessage, ChatMessageToolCall, ChatRole } from './openai';
+import { PromptMetadata } from './results';
+import { ITokenizer } from './tokenizer/tokenizer';
+
+export interface IMaterializedNode {
+	/**
+	 * Gets the maximum number of tokens this message can contain. This is
+	 * calculated by summing the token counts of all individual messages, which
+	 * may be larger than the real count due to merging of sibling tokens.
+	 */
+	upperBoundTokenCount(tokenizer: ITokenizer): Promise<number>;
+
+	/**
+	 * Gets the precise number of tokens this message contains.
+	 */
+	tokenCount(tokenizer: ITokenizer): Promise<number>;
+}
+
+export type MaterializedNode = MaterializedContainer | MaterializedChatMessage | MaterializedChatMessageTextChunk;
+
+export const enum ContainerFlags {
+	/** It's a {@link LegacyPrioritization} instance */
+	IsLegacyPrioritization = 1 << 0,
+	/** It's a {@link Chunk} instance */
+	IsChunk = 1 << 1,
+}
+
+export class MaterializedContainer implements IMaterializedNode {
+
+	constructor(
+		public readonly priority: number,
+		public readonly children: MaterializedNode[],
+		public readonly metadata: PromptMetadata[],
+		public readonly flags: number,
+	) { }
+
+	public has(flag: ContainerFlags) {
+		return !!(this.flags & flag);
+	}
+
+	/** @inheritdoc */
+	async tokenCount(tokenizer: ITokenizer): Promise<number> {
+		let total = 0;
+		await Promise.all(this.children.map(async (child) => {
+			// note: this method is not called when the container is inside a chat
+			// message, because in that case the chat message generates the text
+			// and counts that.
+			assertContainerOrChatMessage(child);
+
+			const amt = await child.tokenCount(tokenizer);
+			total += amt;
+		}));
+		return total;
+	}
+
+	/** @inheritdoc */
+	async upperBoundTokenCount(tokenizer: ITokenizer): Promise<number> {
+		let total = 0;
+		await Promise.all(this.children.map(async (child) => {
+			const amt = await child.upperBoundTokenCount(tokenizer);
+			total += amt;
+		}));
+		return total;
+	}
+
+	/**
+	 * Gets all metadata the container holds.
+	 */
+	allMetadata(): Generator<PromptMetadata> {
+		return allMetadata(this);
+	}
+
+	/**
+	 * Gets the chat messages the container holds.
+	 */
+	*toChatMessages(): Generator<ChatMessage> {
+		for (const child of this.children) {
+			assertContainerOrChatMessage(child);
+			if (child instanceof MaterializedContainer) {
+				yield* child.toChatMessages();
+			} else if (!child.isEmpty) {
+				// note: empty messages are already removed during pruning, but the
+				// consumer might themselves have given us empty messages that we should omit.
+				yield child.toChatMessage();
+			}
+		}
+	}
+
+	/** Removes the node in the tree with the lowest priority. */
+	removeLowestPriorityChild(): void {
+		if (this.has(ContainerFlags.IsLegacyPrioritization)) {
+			removeLowestPriorityLegacy(this);
+		} else {
+			removeLowestPriorityChild(this.children);
+		}
+	}
+}
+
+export const enum LineBreakBefore {
+	None,
+	Always,
+	IfNotTextSibling,
+}
+
+/** A chunk of text in a {@link MaterializedChatMessage} */
+export class MaterializedChatMessageTextChunk {
+	constructor(
+		public readonly text: string,
+		public readonly priority: number,
+		public readonly metadata: PromptMetadata[] = [],
+		public readonly lineBreakBefore: LineBreakBefore,
+	) { }
+
+	public upperBoundTokenCount(tokenizer: ITokenizer) {
+		return this._upperBound(tokenizer);
+	}
+
+	private readonly _upperBound = once(async (tokenizer: ITokenizer) => {
+		return await tokenizer.tokenLength(this.text) + (this.lineBreakBefore !== LineBreakBefore.None ? 1 : 0);
+	});
+}
+
+export class MaterializedChatMessage implements IMaterializedNode {
+
+	constructor(
+		public readonly role: ChatRole,
+		public readonly name: string | undefined,
+		public readonly toolCalls: ChatMessageToolCall[] | undefined,
+		public readonly toolCallId: string | undefined,
+		public readonly priority: number,
+		private readonly childIndex: number,
+		public readonly metadata: PromptMetadata[],
+		public readonly children: MaterializedNode[],
+	) { }
+
+	/** @inheritdoc */
+	public async tokenCount(tokenizer: ITokenizer): Promise<number> {
+		return this._tokenCount(tokenizer);
+	}
+
+	/** @inheritdoc */
+	public async upperBoundTokenCount(tokenizer: ITokenizer): Promise<number> {
+		return this._upperBound(tokenizer);
+	}
+
+	/** Gets the text this message contains */
+	public get text(): string {
+		return this._text()
+	}
+
+	/** Gets whether the message is empty */
+	public get isEmpty() {
+		return !/\S/.test(this.text);
+	}
+
+	/** Remove the lowest priority chunk among this message's children. */
+	removeLowestPriorityChild() {
+		removeLowestPriorityChild(this.children);
+		this.onChunksChange();
+	}
+
+	onChunksChange() {
+		this._tokenCount.clear();
+		this._upperBound.clear();
+		this._text.clear();
+	}
+
+	private readonly _tokenCount = once(async (tokenizer: ITokenizer) => {
+		return tokenizer.countMessageTokens(this.toChatMessage());
+	});
+
+	private readonly _upperBound = once(async (tokenizer: ITokenizer) => {
+		let total = await this._baseMessageTokenCount(tokenizer)
+		await Promise.all(this.children.map(async (chunk) => {
+			const amt = await chunk.upperBoundTokenCount(tokenizer);
+			total += amt;
+		}));
+		return total;
+	});
+
+	private readonly _baseMessageTokenCount = once((tokenizer: ITokenizer) => {
+		return tokenizer.countMessageTokens({ ...this.toChatMessage(), content: '' });
+	});
+
+	private readonly _text = once(() => {
+		let result = '';
+		for (const { text, isTextSibling } of textChunks(this)) {
+			if (text.lineBreakBefore === LineBreakBefore.Always || (text.lineBreakBefore === LineBreakBefore.IfNotTextSibling && !isTextSibling)) {
+				if (result.length && !result.endsWith('\n')) {
+					result += '\n';
+				}
+			}
+
+			result += text.text;
+		}
+
+		return result.trim();
+	});
+
+	public toChatMessage(): ChatMessage {
+		if (this.role === ChatRole.System) {
+			return {
+				role: this.role,
+				content: this.text,
+				...(this.name ? { name: this.name } : {})
+			};
+		} else if (this.role === ChatRole.Assistant) {
+			return {
+				role: this.role,
+				content: this.text,
+				...(this.toolCalls ? { tool_calls: this.toolCalls } : {}),
+				...(this.name ? { name: this.name } : {})
+			};
+		} else if (this.role === ChatRole.User) {
+			return {
+				role: this.role,
+				content: this.text,
+				...(this.name ? { name: this.name } : {})
+			}
+		} else if (this.role === ChatRole.Tool) {
+			return {
+				role: this.role,
+				content: this.text,
+				tool_call_id: this.toolCallId
+			};
+		} else {
+			return {
+				role: this.role,
+				content: this.text,
+				name: this.name!
+			};
+		}
+	}
+
+	public static cmp(a: MaterializedChatMessage, b: MaterializedChatMessage): number {
+		if (a.priority !== b.priority) {
+			return (b.priority || 0) - (a.priority || 0);
+		}
+		return b.childIndex - a.childIndex;
+	}
+}
+
+function assertContainerOrChatMessage(v: MaterializedNode): asserts v is MaterializedContainer | MaterializedChatMessage {
+	if (!(v instanceof MaterializedContainer) && !(v instanceof MaterializedChatMessage)) {
+		throw new Error(`Cannot have a text node outside a ChatMessage. Text: "${v.text}"`);
+	}
+}
+
+
+function* textChunks(node: MaterializedContainer | MaterializedChatMessage, isTextSibling = false): Generator<{ text: MaterializedChatMessageTextChunk; isTextSibling: boolean }> {
+	for (const child of node.children) {
+		if (child instanceof MaterializedChatMessageTextChunk) {
+			yield { text: child, isTextSibling };
+			isTextSibling = true;
+		} else {
+			yield* textChunks(child, isTextSibling);
+			isTextSibling = false;
+		}
+	}
+}
+
+function removeLowestPriorityLegacy(root: MaterializedNode) {
+	let lowest: undefined | {
+		chain: (MaterializedContainer | MaterializedChatMessage)[],
+		node: MaterializedChatMessageTextChunk;
+	};
+
+	function findLowestInTree(node: MaterializedNode, chain: (MaterializedContainer | MaterializedChatMessage)[]) {
+		if (node instanceof MaterializedChatMessageTextChunk) {
+			if (!lowest || node.priority < lowest.node.priority) {
+				lowest = { chain: chain.slice(), node };
+			}
+		} else {
+			chain.push(node);
+			for (const child of node.children) {
+				findLowestInTree(child, chain);
+			}
+			chain.pop();
+		}
+	}
+
+	findLowestInTree(root, []);
+
+	if (!lowest) {
+		throw new Error('No lowest priority node found');
+	}
+
+	let needle: MaterializedNode = lowest.node;
+	let i = lowest.chain.length - 1;
+	for (; i >= 0; i--) {
+		const node = lowest.chain[i];
+		node.children.splice(node.children.indexOf(needle), 1);
+		if (node instanceof MaterializedChatMessage) {
+			node.onChunksChange();
+		}
+		if (node.children.length > 0) {
+			break;
+		}
+
+		needle = node;
+	}
+
+	for (; i >= 0; i--) {
+		const node = lowest.chain[i];
+		if (node instanceof MaterializedChatMessage) {
+			node.onChunksChange();
+		}
+	}
+}
+
+function removeLowestPriorityChild(children: MaterializedNode[]) {
+	if (!children.length) {
+		return;
+	}
+
+	let lowestIndex = 0;
+	let lowestNestedChildPriority: number | undefined;
+	for (let i = 1; i < children.length; i++) {
+		if (children[i].priority < children[lowestIndex].priority) {
+			lowestIndex = i;
+			lowestNestedChildPriority = undefined;
+		} else if (children[i].priority === children[lowestIndex].priority) {
+			// Use the lowest priority of any of their nested remaining children as a tiebreaker,
+			// useful e.g. when dealing with root sibling user vs. system messages
+			lowestNestedChildPriority ??= getLowestPriorityAmongChildren(children[lowestIndex]);
+			const lowestNestedPriority = getLowestPriorityAmongChildren(children[i]);
+			if (lowestNestedPriority < lowestNestedChildPriority) {
+				lowestIndex = i;
+				lowestNestedChildPriority = lowestNestedPriority;
+			}
+		}
+	}
+
+	const lowest = children[lowestIndex];
+	if (lowest instanceof MaterializedChatMessageTextChunk || (lowest instanceof MaterializedContainer && lowest.has(ContainerFlags.IsChunk))) {
+		children.splice(lowestIndex, 1);
+	} else {
+		lowest.removeLowestPriorityChild();
+		if (lowest.children.length === 0) {
+			children.splice(lowestIndex, 1);
+		}
+	}
+}
+
+function getLowestPriorityAmongChildren(node: MaterializedNode): number {
+	if (node instanceof MaterializedChatMessageTextChunk) {
+		return -1;
+	}
+
+	let lowest = Number.MAX_SAFE_INTEGER;
+	for (const child of node.children) {
+		lowest = Math.min(lowest, child.priority);
+	}
+
+	return lowest;
+}
+
+function* allMetadata(node: MaterializedContainer | MaterializedChatMessage): Generator<PromptMetadata> {
+	yield* node.metadata;
+	for (const child of node.children) {
+		if (child instanceof MaterializedChatMessageTextChunk) {
+			yield* child.metadata;
+		} else {
+			yield* allMetadata(child);
+		}
+	}
+}
diff --git a/src/base/once.ts b/src/base/once.ts
new file mode 100644
index 0000000..ac79b78
--- /dev/null
+++ b/src/base/once.ts
@@ -0,0 +1,22 @@
+/*---------------------------------------------------------------------------------------------
+ *  Copyright (c) Microsoft Corporation and GitHub. All rights reserved.
+ *--------------------------------------------------------------------------------------------*/
+
+export function once<T extends (...args: any[]) => any>(fn: T): T & { clear: () => void } {
+	let result: ReturnType<T>;
+	let called = false;
+
+	const wrappedFunction = ((...args: Parameters<T>): ReturnType<T> => {
+		if (!called) {
+			result = fn(...args);
+			called = true;
+		}
+		return result;
+	}) as T & { clear: () => void };
+
+	wrappedFunction.clear = () => {
+		called = false;
+	};
+
+	return wrappedFunction;
+}
diff --git a/src/base/promptElements.tsx b/src/base/promptElements.tsx
index 67acf4d..759e966 100644
--- a/src/base/promptElements.tsx
+++ b/src/base/promptElements.tsx
@@ -4,7 +4,6 @@
 
 import type { CancellationToken } from 'vscode';
 import { contentType } from '.';
-import * as JSONT from './jsonTypes';
 import { ChatRole } from './openai';
 import { PromptElement } from './promptElement';
 import { BasePromptElementProps, PromptPiece, PromptSizing } from './types';
@@ -232,12 +231,22 @@ export class PrioritizedList extends PromptElement<PrioritizedListProps> {
 		return (
 			<>
 				{children.map((child, i) => {
-					child.props ??= {};
-					child.props.priority = this.props.descending
+					if (!child) {
+						return;
+					}
+
+					const priority = this.props.descending
 						? // First element in array of children has highest priority
 						this.props.priority - i
 						: // Last element in array of children has highest priority
 						this.props.priority - children.length + i;
+
+					if (typeof child !== 'object') {
+						return <TextChunk priority={priority}>{child}</TextChunk>;
+					}
+
+					child.props ??= {};
+					child.props.priority = priority;
 					return child;
 				})}
 			</>
@@ -264,43 +273,33 @@ export class ToolResult extends PromptElement<IToolResultProps> {
 	render(): Promise<PromptPiece | undefined> | PromptPiece | undefined {
 		// note: future updates to content types should be handled here for backwards compatibility
 		if (this.props.data.hasOwnProperty(contentType)) {
-			return <elementJSON data={this.rebasePriority(this.props.data[contentType])} />;
+			return <elementJSON data={this.props.data[contentType]} />;
 		} else {
 			return <UserMessage priority={this.priority}>{this.props.data.toString()}</UserMessage>;
 		}
 	}
+}
 
-	/**
-	 * Modifies priorities of all elements in the tree to fractional increments
-	 * past `this.priorty`.
-	 */
-	private rebasePriority(data: JSONT.PromptElementJSON) {
-		if (this.priority === undefined) {
-			return data;
-		}
-
-		const cloned = structuredClone(data);
+/**
+ * Marker element that uses the legacy global prioritization algorithm (0.2.x
+ * if this library) for pruning child elements. This will be removed in
+ * the future.
+ *
+ * @deprecated
+ */
+export class LegacyPrioritization extends PromptElement {
+	render() {
+		return <>{this.props.children}</>;
+	}
+}
 
-		let maxPriorityInChildren = 1;
-		JSONT.forEachNode(cloned.node, node => {
-			// was initially undefined in the tree and was set to this implicitly:
-			if (node.priority === Number.MAX_SAFE_INTEGER) {
-				node.priority = undefined;
-			}
-			if (node.priority !== undefined) {
-				maxPriorityInChildren = Math.max(maxPriorityInChildren, node.priority);
-			}
-		});
-
-		// Elements without priority default to MAX_SAFE_INTEGER in the renderer,
-		// so follow similar behavior here. The denominator of the fractional part
-		// is set so that we maximal elements are `this.priority + (max + 1) / (max + 2)`,
-		// keeping `this.priority <= node.priority < this.priority + 1`
-		JSONT.forEachNode(cloned.node, node => {
-			const frac = (node.priority ?? (maxPriorityInChildren + 1)) / (maxPriorityInChildren + 2);
-			node.priority = this.priority + frac;
-		});
-
-		return cloned;
+/**
+ * Marker element that ensures all of its children are either included, or
+ * not included. This is similar to the `<TextChunk />` element, but it is more
+ * basic and can contain extrinsic children.
+ */
+export class Chunk extends PromptElement<BasePromptElementProps> {
+	render() {
+		return <>{this.props.children}</>;
 	}
 }
diff --git a/src/base/promptRenderer.ts b/src/base/promptRenderer.ts
index 1d275ef..97e55ca 100644
--- a/src/base/promptRenderer.ts
+++ b/src/base/promptRenderer.ts
@@ -5,14 +5,14 @@
 import type { CancellationToken, Progress } from "vscode";
 import * as JSONT from './jsonTypes';
 import { PromptNodeType } from './jsonTypes';
-import { ChatMessage, ChatMessageToolCall, ChatRole } from "./openai";
+import { ContainerFlags, LineBreakBefore, MaterializedChatMessage, MaterializedChatMessageTextChunk, MaterializedContainer } from './materialized';
+import { ChatMessage } from "./openai";
 import { PromptElement } from "./promptElement";
-import { AssistantMessage, BaseChatMessage, ChatMessagePromptElement, TextChunk, ToolMessage, isChatMessagePromptElement } from "./promptElements";
+import { AssistantMessage, BaseChatMessage, ChatMessagePromptElement, Chunk, LegacyPrioritization, TextChunk, ToolMessage, isChatMessagePromptElement } from "./promptElements";
 import { PromptMetadata, PromptReference } from "./results";
 import { ITokenizer } from "./tokenizer/tokenizer";
 import { ITracer } from './tracer';
 import { BasePromptElementProps, IChatEndpointInfo, PromptElementCtor, PromptPiece, PromptPieceChild, PromptSizing } from "./types";
-import { coalesce } from "./util/arrays";
 import { URI } from "./util/vs/common/uri";
 import { ChatDocumentContext, ChatResponsePart } from "./vscodeTypes";
 
@@ -20,6 +20,7 @@ export interface RenderPromptResult {
 	readonly messages: ChatMessage[];
 	readonly tokenCount: number;
 	readonly hasIgnoredFiles: boolean;
+	readonly metadata: MetadataMap;
 	/**
 	 * The references that survived prioritization in the rendered {@link RenderPromptResult.messages messages}.
 	 */
@@ -55,12 +56,9 @@ export namespace MetadataMap {
  */
 export class PromptRenderer<P extends BasePromptElementProps> {
 
-	// map the constructor to the meta data instances
-	private readonly _meta: Map<new () => PromptMetadata, PromptMetadata> = new Map();
 	private readonly _usedContext: ChatDocumentContext[] = [];
 	private readonly _ignoredFiles: URI[] = [];
 	private readonly _root = new PromptTreeElement(null, 0);
-	private readonly _references: PromptReference[] = [];
 	public tracer: ITracer | undefined = undefined;
 
 	/**
@@ -76,23 +74,10 @@ export class PromptRenderer<P extends BasePromptElementProps> {
 		private readonly _tokenizer: ITokenizer
 	) { }
 
-	public getAllMeta(): MetadataMap {
-		const metadataMap = this._meta;
-		return {
-			get<T extends PromptMetadata>(key: new (...args: any[]) => T): T | undefined {
-				return metadataMap.get(key) as T | undefined;
-			}
-		};
-	}
-
 	public getIgnoredFiles(): URI[] {
 		return Array.from(new Set(this._ignoredFiles));
 	}
 
-	public getMeta<T extends PromptMetadata>(key: new (...args: any[]) => T): T | undefined {
-		return this._meta.get(key) as T | undefined;
-	}
-
 	public getUsedContext(): ChatDocumentContext[] {
 		return this._usedContext;
 	}
@@ -223,56 +208,6 @@ export class PromptRenderer<P extends BasePromptElementProps> {
 		this.tracer?.endRenderPass();
 	}
 
-	private async _prioritize<T extends Countable>(things: T[], cmp: (a: T, b: T) => number, count: (thing: T) => Promise<number>) {
-		const prioritizedChunks: { index: number; precedingLinebreak?: number }[] = []; // sorted by descending priority
-		const chunkResult: (T | null)[] = [];
-
-		let i = 0;
-		while (i < things.length) {
-			// We only consider non-linebreaks for prioritization
-			if (!things[i].isImplicitLinebreak) {
-				const chunk = things[i - 1]?.isImplicitLinebreak ? { index: i, precedingLinebreak: i - 1 } : { index: i };
-				prioritizedChunks.push(chunk);
-				chunkResult[i] = null;
-			}
-			i += 1;
-		}
-
-		prioritizedChunks.sort((a, b) => cmp(things[a.index], things[b.index]));
-
-		let remainingBudget = this._endpoint.modelMaxPromptTokens;
-		const omittedChunks: T[] = [];
-		while (prioritizedChunks.length > 0) {
-			const prioritizedChunk = prioritizedChunks.shift()!;
-			const index = prioritizedChunk.index;
-			const chunk = things[index];
-			let tokenCount = await count(chunk);
-			let precedingLinebreak;
-			if (prioritizedChunk.precedingLinebreak) {
-				precedingLinebreak = things[prioritizedChunk.precedingLinebreak];
-				tokenCount += await count(precedingLinebreak);
-			}
-			if (tokenCount > remainingBudget) {
-				// Wouldn't fit anymore
-				omittedChunks.push(chunk);
-				break;
-			}
-			chunkResult[index] = chunk;
-			if (prioritizedChunk.precedingLinebreak && precedingLinebreak) {
-				chunkResult[prioritizedChunk.precedingLinebreak] = precedingLinebreak;
-			}
-			remainingBudget -= tokenCount;
-		}
-
-		for (const omittedChunk of prioritizedChunks) {
-			const index = omittedChunk.index;
-			const chunk = things[index];
-			omittedChunks.push(chunk);
-		}
-
-		return { result: coalesce(chunkResult), tokenCount: this._endpoint.modelMaxPromptTokens - remainingBudget, omittedChunks };
-	}
-
 	/**
 	 * Renders the prompt element and its children to a JSON-serializable state.
 	 * @returns A promise that resolves to an object containing the rendered chat messages and the total token count.
@@ -306,87 +241,70 @@ export class PromptRenderer<P extends BasePromptElementProps> {
 			token,
 		);
 
-		// Convert prompt pieces to message chunks (text and linebreaks)
-		const { result: messageChunks, resultChunks } = this._root.materialize();
-
-		// First pass: sort message chunks by priority. Note that this can yield an imprecise result due to token boundaries within a single chat message
-		// so we also need to do a second pass over the full chat messages later
-		const chunkMessages = new Set<MaterializedChatMessage>();
-		const { result: prioritizedChunks, omittedChunks } = await this._prioritize(
-			resultChunks,
-			(a, b) => MaterializedChatMessageTextChunk.cmp(a, b),
-			async (chunk) => {
-				let tokenLength = await this._tokenizer.tokenLength(chunk.text);
-				if (!chunkMessages.has(chunk.message)) {
-					chunkMessages.add(chunk.message);
-					tokenLength = await this._tokenizer.countMessageTokens(chunk.toChatMessage());
-				}
-				return tokenLength;
-			});
-
-		// Update chat messages with their chunks that survived prioritization
-		const chatMessagesToChunks = new Map<MaterializedChatMessage, MaterializedChatMessageTextChunk[]>();
-		for (const chunk of coalesce(prioritizedChunks)) {
-			const value = chatMessagesToChunks.get(chunk.message) ?? [];
-			value[chunk.childIndex] = chunk;
-			chatMessagesToChunks.set(chunk.message, value);
+		// Trim the elements to fit within the token budget. We check the "lower bound"
+		// first because that's much more cache-friendly as we remove elements.
+		const container = this._root.materialize() as MaterializedContainer;
+		const allMetadata = [...container.allMetadata()];
+		while (
+			await container.upperBoundTokenCount(this._tokenizer) > this._endpoint.modelMaxPromptTokens &&
+			await container.tokenCount(this._tokenizer) > this._endpoint.modelMaxPromptTokens
+		) {
+			container.removeLowestPriorityChild();
 		}
 
-		// Collect chat messages with surviving prioritized chunks in the order they were declared
-		const chatMessages: MaterializedChatMessage[] = [];
-		for (const message of messageChunks) {
-			const chunks = chatMessagesToChunks.get(message);
-			if (chunks) {
-				message.chunks = coalesce(chunks);
-				for (const chunk of chunks) {
-					if (chunk && chunk.references.length > 0) {
-						message.references.push(...chunk.references);
-					}
-				}
-				chatMessages.push(message);
-			}
-		}
-
-		// Second pass: make sure the chat messages will fit within the token budget
-		const { result: prioritizedMaterializedChatMessages, tokenCount } = await this._prioritize(chatMessages, (a, b) => MaterializedChatMessage.cmp(a, b), async (message) => this._tokenizer.countMessageTokens(message.toChatMessage()));
-
 		// Then finalize the chat messages
-		const messageResult = prioritizedMaterializedChatMessages.map(message => message?.toChatMessage());
+		const messageResult = [...container.toChatMessages()];
+		const tokenCount = await container.tokenCount(this._tokenizer);
+		const remainingMetadata = [...container.allMetadata()];
 
 		// Remove undefined and duplicate references
-		const { references, names } = prioritizedMaterializedChatMessages.reduce<{ references: PromptReference[], names: Set<string> }>((acc, message) => {
-			[...this._references, ...message.references].forEach((ref) => {
-				const isVariableName = 'variableName' in ref.anchor;
-				if (isVariableName && !acc.names.has(ref.anchor.variableName)) {
-					acc.references.push(ref);
-					acc.names.add(ref.anchor.variableName);
-				} else if (!isVariableName) {
-					acc.references.push(ref);
-				}
-			});
-			return acc;
-		}, { references: [], names: new Set<string>() });
+		const referenceNames = new Set<string>();
+		const references = remainingMetadata.map(m => {
+			if (!(m instanceof ReferenceMetadata)) {
+				return;
+			}
+
+			const ref = m.reference;
+			const isVariableName = 'variableName' in ref.anchor;
+			if (isVariableName && !referenceNames.has(ref.anchor.variableName)) {
+				referenceNames.add(ref.anchor.variableName);
+				return ref;
+			} else if (!isVariableName) {
+				return ref;
+			}
+		}).filter(isDefined);
 
 		// Collect the references for chat message chunks that did not survive prioritization
-		const { references: omittedReferences } = omittedChunks.reduce<{ references: PromptReference[] }>((acc, message) => {
-			message.references.forEach((ref) => {
-				const isVariableName = 'variableName' in ref.anchor;
-				if (isVariableName && !names.has(ref.anchor.variableName)) {
-					acc.references.push(ref);
-					names.add(ref.anchor.variableName);
-				} else if (!isVariableName) {
-					acc.references.push(ref);
-				}
-			});
-			return acc;
-		}, { references: [] });
+		const omittedReferences = allMetadata.map(m => {
+			if (!(m instanceof ReferenceMetadata) || remainingMetadata.includes(m)) {
+				return;
+			}
+
+			const ref = m.reference;
+			const isVariableName = 'variableName' in ref.anchor;
+			if (isVariableName && !referenceNames.has(ref.anchor.variableName)) {
+				referenceNames.add(ref.anchor.variableName);
+				return ref;
+			} else if (!isVariableName) {
+				return ref;
+			}
+		}).filter(isDefined);
 
-		return { messages: messageResult, hasIgnoredFiles: this._ignoredFiles.length > 0, tokenCount, references: coalesce(references), omittedReferences: coalesce(omittedReferences) };
+		return {
+			metadata: {
+				get: ctor => remainingMetadata.find(m => m instanceof ctor) as any
+			},
+			messages: messageResult,
+			hasIgnoredFiles: this._ignoredFiles.length > 0,
+			tokenCount,
+			references,
+			omittedReferences,
+		};
 	}
 
 	private _handlePromptChildren(element: QueueItem<PromptElementCtor<any, any>, P>, pieces: ProcessedPromptPiece[], sizing: PromptSizingContext, progress: Progress<ChatResponsePart> | undefined, token: CancellationToken | undefined) {
 		if (element.ctor === TextChunk) {
-			this._handleExtrinsicTextChunkChildren(element.node.parent!, element.node, element.props, pieces);
+			this._handleExtrinsicTextChunkChildren(element.node, element.node, element.props, pieces);
 			return;
 		}
 
@@ -431,18 +349,19 @@ export class PromptRenderer<P extends BasePromptElementProps> {
 		if (children.length > 0) {
 			throw new Error(`<meta /> must not have children!`);
 		}
-		const key = Object.getPrototypeOf(props.value).constructor;
-		if (this._meta.has(key)) {
-			throw new Error(`Duplicate metadata ${key.name}!`);
+
+		if (props.local) {
+			node.addMetadata(props.value);
+		} else {
+			this._root.addMetadata(props.value);
 		}
-		this._meta.set(key, props.value);
 	}
 
 	private _handleIntrinsicLineBreak(node: PromptTreeElement, props: JSX.IntrinsicElements['br'], children: ProcessedPromptPiece[], inheritedPriority?: number, sortIndex?: number) {
 		if (children.length > 0) {
 			throw new Error(`<br /> must not have children!`);
 		}
-		node.appendLineBreak(true, inheritedPriority ?? Number.MAX_SAFE_INTEGER, sortIndex);
+		node.appendLineBreak(inheritedPriority ?? Number.MAX_SAFE_INTEGER, sortIndex);
 	}
 
 	private _handleIntrinsicElementJSON(node: PromptTreeElement, data: JSONT.PromptElementJSON) {
@@ -460,8 +379,9 @@ export class PromptRenderer<P extends BasePromptElementProps> {
 		if (children.length > 0) {
 			throw new Error(`<reference /> must not have children!`);
 		}
-		node.addReferences(props.value);
-		this._references.push(...props.value);
+		for (const ref of props.value) {
+			node.addMetadata(new ReferenceMetadata(ref));
+		}
 	}
 
 
@@ -481,7 +401,7 @@ export class PromptRenderer<P extends BasePromptElementProps> {
 	 */
 	private _handleExtrinsicTextChunkChildren(node: PromptTreeElement, textChunkNode: PromptTreeElement, props: BasePromptElementProps, children: ProcessedPromptPiece[]) {
 		const content: string[] = [];
-		const references: PromptReference[] = [];
+		const metadata: PromptMetadata[] = [];
 
 		for (const child of children) {
 			if (child.kind === 'extrinsic') {
@@ -498,15 +418,16 @@ export class PromptRenderer<P extends BasePromptElementProps> {
 					content.push('\n');
 				} else if (child.name === 'references') {
 					// For TextChunks, references must be propagated through the PromptText element that is appended to the node
-					references.push(...child.props.value);
+					for (const reference of child.props.value) {
+						metadata.push(new ReferenceMetadata(reference));
+					}
 				} else {
 					this._handleIntrinsic(node, child.name, child.props, flattenAndReduceArr(child.children), textChunkNode.childIndex);
 				}
 			}
 		}
 
-		node.appendLineBreak(false, undefined, textChunkNode.childIndex);
-		node.appendStringChild(content.join(''), props?.priority ?? Number.MAX_SAFE_INTEGER, references, textChunkNode.childIndex);
+		node.appendStringChild(content.join(''), props?.priority ?? Number.MAX_SAFE_INTEGER, metadata, textChunkNode.childIndex, true);
 	}
 }
 
@@ -583,8 +504,8 @@ class LiteralPromptPiece {
 
 type ProcessedPromptPiece = LiteralPromptPiece | IntrinsicPromptPiece<any> | ExtrinsicPromptPiece<any, any>;
 
-type PromptNode = PromptTreeElement | PromptText | PromptLineBreak;
-type LeafPromptNode = PromptText | PromptLineBreak;
+type PromptNode = PromptTreeElement | PromptText;
+type LeafPromptNode = PromptText;
 
 /**
  * A shared instance given to each PromptTreeElement that contains information
@@ -615,15 +536,13 @@ class PromptSizingContext {
 class PromptTreeElement {
 	public static fromJSON(index: number, json: JSONT.PieceJSON): PromptTreeElement {
 		const element = new PromptTreeElement(null, index);
-		element._references = json.references?.map(r => PromptReference.fromJSON(r)) ?? [];
+		element._metadata = json.references?.map(r => new ReferenceMetadata(PromptReference.fromJSON(r))) ?? [];
 		element._children = json.children.map((childJson, i) => {
 			switch (childJson.type) {
 				case JSONT.PromptNodeType.Piece:
 					return PromptTreeElement.fromJSON(i, childJson);
 				case JSONT.PromptNodeType.Text:
 					return PromptText.fromJSON(element, i, childJson);
-				case JSONT.PromptNodeType.LineBreak:
-					return PromptLineBreak.fromJSON(element, i, childJson);
 				default:
 					softAssertNever(childJson);
 			}
@@ -647,7 +566,7 @@ class PromptTreeElement {
 	private _obj: PromptElement | null = null;
 	private _state: any | undefined = undefined;
 	private _children: PromptNode[] = [];
-	private _references: PromptReference[] = [];
+	private _metadata: PromptMetadata[] = [];
 
 	constructor(
 		public readonly parent: PromptTreeElement | null = null,
@@ -678,19 +597,12 @@ class PromptTreeElement {
 		return child;
 	}
 
-	public appendStringChild(text: string, priority?: number, references?: PromptReference[], sortIndex = this._children.length) {
-		this._children.push(new PromptText(this, sortIndex, text, priority, references));
+	public appendStringChild(text: string, priority?: number, metadata?: PromptMetadata[], sortIndex = this._children.length, lineBreakBefore = false) {
+		this._children.push(new PromptText(this, sortIndex, text, priority, metadata, lineBreakBefore));
 	}
 
-	public appendLineBreak(explicit = true, priority?: number, sortIndex = this._children.length): void {
-		this._children.push(new PromptLineBreak(this, sortIndex, explicit, priority));
-	}
-
-	public materialize(): { result: MaterializedChatMessage[]; resultChunks: MaterializedChatMessageTextChunk[] } {
-		const result: MaterializedChatMessage[] = [];
-		const resultChunks: MaterializedChatMessageTextChunk[] = [];
-		this._materialize(result, resultChunks);
-		return { result, resultChunks };
+	public appendLineBreak(priority?: number, sortIndex = this._children.length): void {
+		this._children.push(new PromptText(this, sortIndex, '\n', priority));
 	}
 
 	public toJSON(): JSONT.PieceJSON {
@@ -699,7 +611,7 @@ class PromptTreeElement {
 			ctor: JSONT.PieceCtorKind.Other,
 			children: this._children.slice().sort((a, b) => a.childIndex - b.childIndex).map(c => c.toJSON()),
 			priority: this._obj?.props.priority,
-			references: this._references?.map(r => r.toJSON()),
+			references: this._metadata.filter(m => m instanceof ReferenceMetadata).map(r => r.reference.toJSON()),
 		};
 
 		if (this._obj instanceof BaseChatMessage) {
@@ -716,182 +628,46 @@ class PromptTreeElement {
 		return json;
 	}
 
-	private _materialize(result: MaterializedChatMessage[], resultChunks: MaterializedChatMessageTextChunk[]): void {
+	public materialize(): MaterializedChatMessage | MaterializedContainer {
 		this._children.sort((a, b) => a.childIndex - b.childIndex);
 		if (this._obj instanceof BaseChatMessage) {
 			if (!this._obj.props.role) {
 				throw new Error(`Invalid ChatMessage!`);
 			}
-			const leafNodes: LeafPromptNode[] = [];
-			for (const child of this._children) {
-				child.collectLeafs(leafNodes);
-			}
-			const chunks: MaterializedChatMessageTextChunk[] = [];
 			const parent = new MaterializedChatMessage(
 				this._obj.props.role,
 				this._obj.props.name,
 				this._obj instanceof AssistantMessage ? this._obj.props.toolCalls : undefined,
 				this._obj instanceof ToolMessage ? this._obj.props.toolCallId : undefined,
-				this._obj.props.priority,
+				this._obj.props.priority ?? 0,
 				this.childIndex,
-				chunks
+				this._metadata,
+				this._children.map(child => child.materialize()),
 			);
-			let childIndex = resultChunks.length;
-			leafNodes.forEach((node, index) => {
-				if (node.kind === PromptNodeType.Text) {
-					chunks.push(new MaterializedChatMessageTextChunk(parent, node.text, node.priority, childIndex++, false, node.references ?? this._references));
-				} else {
-					if (node.isExplicit) {
-						chunks.push(new MaterializedChatMessageTextChunk(parent, '\n', node.priority, childIndex++));
-					} else if (chunks.length > 0 && chunks[chunks.length - 1].text !== '\n' || chunks[index - 1] && chunks[index - 1].text !== '\n') {
-						// Only insert an implicit linebreak if there wasn't already an explicit linebreak before
-						chunks.push(new MaterializedChatMessageTextChunk(parent, '\n', node.priority, childIndex++, true));
-					}
-				}
-			});
-			resultChunks.push(...chunks);
-			result.push(parent);
+			return parent;
 		} else {
-			for (const child of this._children) {
-				if (child.kind === PromptNodeType.Text) {
-					throw new Error(`Cannot have a text node outside a ChatMessage. Text: "${child.text}"`);
-				} else if (child.kind === PromptNodeType.LineBreak) {
-					throw new Error(`Cannot have a line break node outside a ChatMessage!`);
-				}
-				child._materialize(result, resultChunks);
-			}
-		}
-	}
-
-	public collectLeafs(result: LeafPromptNode[]): void {
-		if (this._obj instanceof BaseChatMessage) {
-			throw new Error(`Cannot have a ChatMessage nested inside a ChatMessage!`);
-		}
-		if (this._obj?.insertLineBreakBefore) {
-			// Add an implicit <br/> before the element
-			result.push(new PromptLineBreak(this, 0, false));
-		}
-		for (const child of this._children.sort((a, b) => a.childIndex - b.childIndex)) {
-			child.collectLeafs(result);
-		}
-	}
-
-	public addReferences(references: PromptReference[]): void {
-		this._references.push(...references);
-	}
-}
-
-interface Countable {
-	text: string;
-	isImplicitLinebreak?: boolean;
-}
-
-class MaterializedChatMessageTextChunk implements Countable {
-	constructor(
-		public readonly message: MaterializedChatMessage,
-		public readonly text: string,
-		private readonly priority: number | undefined,
-		public readonly childIndex: number,
-		public readonly isImplicitLinebreak = false,
-		public readonly references: PromptReference[] = []
-	) { }
-
-	public static cmp(a: MaterializedChatMessageTextChunk, b: MaterializedChatMessageTextChunk): number {
-		if (a.priority !== undefined && b.priority !== undefined && a.priority === b.priority) {
-			// If the chunks share the same parent, break priority ties based on the order
-			// that the chunks were declared in under its parent chat message
-			if (a.message === b.message) {
-				return a.childIndex - b.childIndex;
-			}
-			// Otherwise, prioritize chunks that were declared last
-			return b.childIndex - a.childIndex;
-		}
-
-		if (a.priority !== undefined && b.priority !== undefined && a.priority !== b.priority) {
-			return b.priority - a.priority;
+			let flags = 0;
+			if (this._obj instanceof LegacyPrioritization) flags |= ContainerFlags.IsLegacyPrioritization;
+			if (this._obj instanceof Chunk) flags |= ContainerFlags.IsChunk;
+
+			return new MaterializedContainer(
+				this._obj?.props.priority || 0,
+				this._children.map(child => child.materialize()),
+				this._metadata,
+				flags,
+			);
 		}
-
-		return a.childIndex - b.childIndex;
 	}
 
-	public toChatMessage(): ChatMessage {
-		const chatMessage = this.message.toChatMessage();
-		chatMessage.content = this.text;
-		return chatMessage;
+	public addMetadata(metadata: PromptMetadata): void {
+		this._metadata.push(metadata);
 	}
 }
 
-class MaterializedChatMessage implements Countable {
-	constructor(
-		public readonly role: ChatRole,
-		public readonly name: string | undefined,
-		public readonly toolCalls: ChatMessageToolCall[] | undefined,
-		public readonly toolCallId: string | undefined,
-		private readonly priority: number | undefined,
-		private readonly childIndex: number,
-		private _chunks: MaterializedChatMessageTextChunk[],
-		public references: PromptReference[] = []
-	) { }
-
-	public set chunks(chunks: MaterializedChatMessageTextChunk[]) {
-		this._chunks = chunks;
-	}
-
-	public get text(): string {
-		return this._chunks.reduce((acc, c, i) => {
-			if (i !== (this._chunks.length - 1) || !c.isImplicitLinebreak) {
-				acc += c.text;
-			}
-			return acc;
-		}, '');
-	}
-
-	public toChatMessage(): ChatMessage {
-		if (this.role === ChatRole.System) {
-			return {
-				role: this.role,
-				content: this.text,
-				...(this.name ? { name: this.name } : {})
-			};
-		} else if (this.role === ChatRole.Assistant) {
-			return {
-				role: this.role,
-				content: this.text,
-				...(this.toolCalls ? { tool_calls: this.toolCalls } : {}),
-				...(this.name ? { name: this.name } : {})
-			};
-		} else if (this.role === ChatRole.User) {
-			return {
-				role: this.role,
-				content: this.text,
-				...(this.name ? { name: this.name } : {})
-			}
-		} else if (this.role === ChatRole.Tool) {
-			return {
-				role: this.role,
-				content: this.text,
-				tool_call_id: this.toolCallId
-			};
-		} else {
-			return {
-				role: this.role,
-				content: this.text,
-				name: this.name!
-			};
-		}
-	}
-
-	public static cmp(a: MaterializedChatMessage, b: MaterializedChatMessage): number {
-		if (a.priority !== b.priority) {
-			return (b.priority || 0) - (a.priority || 0);
-		}
-		return b.childIndex - a.childIndex;
-	}
-}
 
 class PromptText {
 	public static fromJSON(parent: PromptTreeElement, index: number, json: JSONT.TextJSON): PromptText {
-		return new PromptText(parent, index, json.text, json.priority, json.references?.map(r => PromptReference.fromJSON(r)));
+		return new PromptText(parent, index, json.text, json.priority, json.references?.map(r => new ReferenceMetadata(PromptReference.fromJSON(r))), json.lineBreakBefore);
 	}
 
 	public readonly kind = PromptNodeType.Text;
@@ -901,46 +677,30 @@ class PromptText {
 		public readonly childIndex: number,
 		public readonly text: string,
 		public readonly priority?: number,
-		public readonly references?: PromptReference[]
+		public readonly metadata?: PromptMetadata[],
+		public readonly lineBreakBefore = false,
 	) { }
 
 	public collectLeafs(result: LeafPromptNode[]) {
 		result.push(this);
 	}
 
+	public materialize() {
+		const lineBreak = this.lineBreakBefore
+			? LineBreakBefore.Always
+			: this.childIndex === 0
+				? LineBreakBefore.IfNotTextSibling
+				: LineBreakBefore.None;
+		return new MaterializedChatMessageTextChunk(this.text, this.priority ?? Number.MAX_SAFE_INTEGER, this.metadata || [], lineBreak);
+	}
+
 	public toJSON(): JSONT.TextJSON {
 		return {
 			type: JSONT.PromptNodeType.Text,
 			priority: this.priority,
 			text: this.text,
-			references: this.references?.map(r => r.toJSON()),
-		};
-	}
-}
-
-class PromptLineBreak {
-	public static fromJSON(parent: PromptTreeElement, index: number, json: JSONT.LineBreakJSON): PromptLineBreak {
-		return new PromptLineBreak(parent, index, json.isExplicit, json.priority);
-	}
-
-	public readonly kind = PromptNodeType.LineBreak;
-
-	constructor(
-		public readonly parent: PromptTreeElement,
-		public readonly childIndex: number,
-		public readonly isExplicit: boolean,
-		public readonly priority?: number
-	) { }
-
-	public collectLeafs(result: LeafPromptNode[]) {
-		result.push(this);
-	}
-
-	public toJSON(): JSONT.LineBreakJSON {
-		return {
-			type: JSONT.PromptNodeType.LineBreak,
-			isExplicit: this.isExplicit,
-			priority: this.priority,
+			references: this.metadata?.filter(m => m instanceof ReferenceMetadata).map(r => r.reference.toJSON()),
+			lineBreakBefore: this.lineBreakBefore,
 		};
 	}
 }
@@ -957,3 +717,11 @@ function softAssertNever(x: never): void {
 function isDefined<T>(x: T | undefined): x is T {
 	return x !== undefined;
 }
+
+class InternalMetadata extends PromptMetadata { }
+
+class ReferenceMetadata extends InternalMetadata {
+	constructor(public readonly reference: PromptReference) {
+		super();
+	}
+}
diff --git a/src/base/test/materialized.test.ts b/src/base/test/materialized.test.ts
new file mode 100644
index 0000000..0aaf53b
--- /dev/null
+++ b/src/base/test/materialized.test.ts
@@ -0,0 +1,41 @@
+/*---------------------------------------------------------------------------------------------
+ *  Copyright (c) Microsoft Corporation and GitHub. All rights reserved.
+ *--------------------------------------------------------------------------------------------*/
+
+import * as assert from 'assert';
+import { LineBreakBefore, MaterializedChatMessage, MaterializedChatMessageTextChunk, MaterializedContainer } from '../materialized';
+import { ChatRole } from '../openai';
+import { ITokenizer } from '../tokenizer/tokenizer';
+class MockTokenizer implements ITokenizer {
+	tokenLength(text: string): number {
+		return text.length;
+	}
+	countMessageTokens(message: any): number {
+		return message.content.length + 3;
+	}
+}
+suite('Materialized', () => {
+	test('should calculate token count correctly', async () => {
+		const tokenizer = new MockTokenizer();
+		const child1 = new MaterializedChatMessageTextChunk('Hello', 1, [], LineBreakBefore.None);
+		const child2 = new MaterializedChatMessageTextChunk('World', 1, [], LineBreakBefore.None);
+		const message = new MaterializedChatMessage(ChatRole.User, 'user', undefined, undefined, 1, 0, [], [child1, child2]);
+		const container = new MaterializedContainer(1, [message], [], 0);
+
+		assert.deepStrictEqual(await container.tokenCount(tokenizer), 13);
+		container.removeLowestPriorityChild();
+		assert.deepStrictEqual(await container.tokenCount(tokenizer), 8);
+	});
+
+	test('should calculate lower bound token count correctly', async () => {
+		const tokenizer = new MockTokenizer();
+		const child1 = new MaterializedChatMessageTextChunk('Hello', 1, [], LineBreakBefore.None);
+		const child2 = new MaterializedChatMessageTextChunk('World', 1, [], LineBreakBefore.None);
+		const message = new MaterializedChatMessage(ChatRole.User, 'user', undefined, undefined, 1, 0, [], [child1, child2]);
+		const container = new MaterializedContainer(1, [message], [], 0);
+
+		assert.deepStrictEqual(await container.upperBoundTokenCount(tokenizer), 13);
+		container.removeLowestPriorityChild();
+		assert.deepStrictEqual(await container.upperBoundTokenCount(tokenizer), 8);
+	});
+});
diff --git a/src/base/test/renderer.test.tsx b/src/base/test/renderer.test.tsx
index 3794d49..1383c07 100644
--- a/src/base/test/renderer.test.tsx
+++ b/src/base/test/renderer.test.tsx
@@ -8,6 +8,8 @@ import { BaseTokensPerCompletion, ChatMessage, ChatRole } from '../openai';
 import { PromptElement } from '../promptElement';
 import {
 	AssistantMessage,
+	Chunk,
+	LegacyPrioritization,
 	PrioritizedList,
 	SystemMessage,
 	TextChunk,
@@ -16,7 +18,7 @@ import {
 	UserMessage,
 } from '../promptElements';
 import { PromptRenderer, RenderPromptResult } from '../promptRenderer';
-import { PromptReference } from '../results';
+import { PromptMetadata, PromptReference } from '../results';
 import { Cl100KBaseTokenizer } from '../tokenizer/cl100kBaseTokenizer';
 import { ITokenizer } from '../tokenizer/tokenizer';
 import {
@@ -244,6 +246,211 @@ suite('PromptRenderer', () => {
 		]);
 	});
 
+	suite('prunes in priority order', () => {
+		async function assertPruningOrder(elements: PromptPiece, order: string[]) {
+			const initialRender = await new PromptRenderer(
+				{ modelMaxPromptTokens: Number.MAX_SAFE_INTEGER } as any,
+				class extends PromptElement {
+					render() {
+						return elements;
+					}
+				},
+				{},
+				tokenizer
+			).render();
+
+			let tokens = initialRender.tokenCount;
+			let last = '';
+			for (let i = 0; i < order.length;) {
+				const res = await new PromptRenderer(
+					{ modelMaxPromptTokens: tokens } as any,
+					class extends PromptElement {
+						render() {
+							return elements;
+						}
+					},
+					{},
+					tokenizer
+				).render();
+
+				const messages = res.messages.map(m => `${m.role}: ${m.content}`).join('\n');
+				if (messages === last) {
+					tokens--;
+					continue;
+				}
+
+				for (let k = 0; k < i; k++) {
+					if (res.messages.some(m => m.content.includes(order[k]))) {
+						throw new Error(`Expected messages TO NOT HAVE "${order[k]}" at budget of ${tokens}. Got:\n\n${messages}\n\nLast was: ${last}`);
+					}
+				}
+				for (let k = i; k < order.length; k++) {
+					if (!res.messages.some(m => m.content.includes(order[k]))) {
+						throw new Error(`Expected messages TO INCLUDE "${order[k]}" at budget of ${tokens}. Got:\n\n${messages}\n\nLast was: ${last}`);
+					}
+				}
+
+				last = messages;
+				tokens--;
+				i++;
+			}
+		}
+
+		test('basic siblings', async () => {
+			await assertPruningOrder(<>
+				<UserMessage>
+					<TextChunk priority={1}>a</TextChunk>
+					<TextChunk priority={2}>b</TextChunk>
+					<TextChunk priority={3}>c</TextChunk>
+				</UserMessage>
+			</>, ['a', 'b', 'c']);
+		});
+
+		test('chunks together', async () => {
+			await assertPruningOrder(<>
+				<UserMessage>
+					<Chunk priority={1}>
+						<TextChunk priority={1}>a</TextChunk>
+						<TextChunk priority={2}>b</TextChunk>
+					</Chunk>
+					<TextChunk priority={3}>c</TextChunk>
+				</UserMessage>
+			</>, ['a', 'c']); // 'b' should not get individually removed and cause a change
+		});
+
+		test('does not scope priorities in fragments', async () => {
+			await assertPruningOrder(<>
+				<UserMessage>
+					<TextChunk priority={1}>b</TextChunk>
+					<>
+						<TextChunk priority={0}>a</TextChunk>
+						<TextChunk priority={2}>c</TextChunk>
+					</>
+					<TextChunk priority={3}>d</TextChunk>
+				</UserMessage>
+			</>, ['a', 'b', 'c', 'd']);
+		});
+
+		test('scopes priorities normally', async () => {
+			class Wrap1 extends PromptElement {
+				render() {
+					return <>
+						<TextChunk priority={1}>a</TextChunk>
+						<TextChunk priority={10}>b</TextChunk>
+					</>
+				}
+			}
+			class Wrap2 extends PromptElement {
+				render() {
+					return <>
+						<TextChunk priority={2}>c</TextChunk>
+						<TextChunk priority={15}>d</TextChunk>
+					</>
+				}
+			}
+			await assertPruningOrder(<>
+				<UserMessage>
+					<Wrap1 priority={1} />
+					<Wrap2 priority={2} />
+				</UserMessage>
+			</>, ['a', 'b', 'c', 'd']);
+		});
+
+		test('balances priorities of equal children', async () => {
+			class Wrap1 extends PromptElement {
+				render() {
+					return <>
+						<TextChunk priority={1}>a</TextChunk>
+						<TextChunk priority={10}>b</TextChunk>
+					</>
+				}
+			}
+			class Wrap2 extends PromptElement {
+				render() {
+					return <>
+						<TextChunk priority={2}>c</TextChunk>
+						<TextChunk priority={15}>d</TextChunk>
+					</>
+				}
+			}
+			await assertPruningOrder(<>
+				<UserMessage>
+					<Wrap1 />
+					<Wrap2 />
+				</UserMessage>
+			</>, ['a', 'c', 'b', 'd']);
+		});
+
+		test('priority list', async () => {
+			await assertPruningOrder(<UserMessage>
+				<PrioritizedList priority={1} descending={false}>
+					<TextChunk>a</TextChunk>
+					<TextChunk>b</TextChunk>
+					<TextChunk>c</TextChunk>
+				</PrioritizedList>
+				<PrioritizedList priority={2} descending={true}>
+					<TextChunk>d</TextChunk>
+					<TextChunk>e</TextChunk>
+					<TextChunk>f</TextChunk>
+				</PrioritizedList>
+			</UserMessage>, ['a', 'b', 'c', 'f', 'e', 'd']);
+		});
+
+		test('balances priorities of equal across chat messages', async () => {
+			await assertPruningOrder(<>
+				<UserMessage>
+					<TextChunk priority={1}>a</TextChunk>
+					<TextChunk priority={10}>b</TextChunk>
+				</UserMessage>
+				<SystemMessage>
+					<TextChunk priority={2}>c</TextChunk>
+					<TextChunk priority={15}>d</TextChunk>
+				</SystemMessage>
+			</>, ['a', 'c', 'b', 'd']);
+		});
+
+		test('scopes priorities in messages', async () => {
+			await assertPruningOrder(<>
+				<UserMessage priority={1}>
+					<TextChunk priority={1}>a</TextChunk>
+					<TextChunk priority={10}>b</TextChunk>
+				</UserMessage>
+				<SystemMessage priority={2}>
+					<TextChunk priority={2}>c</TextChunk>
+					<TextChunk priority={15}>d</TextChunk>
+				</SystemMessage>
+			</>, ['a', 'b', 'c', 'd']);
+		});
+
+		test('uses legacy prioritization', async () => {
+			class Wrap1 extends PromptElement {
+				render() {
+					return <>
+						<TextChunk priority={1}>a</TextChunk>
+						<TextChunk priority={10}>b</TextChunk>
+					</>
+				}
+			}
+			class Wrap2 extends PromptElement {
+				render() {
+					return <>
+						<TextChunk priority={2}>c</TextChunk>
+						<TextChunk priority={15}>d</TextChunk>
+					</>
+				}
+			}
+			await assertPruningOrder(<LegacyPrioritization>
+				<UserMessage>
+					<Wrap1 priority={1} />
+					<Wrap2 priority={2} />
+				</UserMessage>
+				<UserMessage>
+					<TextChunk priority={5}>e</TextChunk>
+				</UserMessage>
+			</LegacyPrioritization>, ['a', 'c', 'e', 'b', 'd']);
+		});
+	});
+
 	suite('truncates tokens exceeding token budget', async () => {
 		class Prompt1 extends PromptElement {
 			render(_: void, sizing: PromptSizing) {
@@ -694,7 +901,6 @@ suite('PromptRenderer', () => {
 					tokenizer
 				);
 				const res2 = await inst2.render(undefined, undefined);
-				assert.equal(res2.tokenCount, 120 - BaseTokensPerCompletion);
 				assert.deepStrictEqual(res2.messages, [
 					{
 						role: 'system',
@@ -720,160 +926,7 @@ suite('PromptRenderer', () => {
 					},
 					{ role: 'user', content: 'What is your name?' },
 				]);
-			});
-
-			test('are globally prioritized across messages', async () => {
-				class TextChunkPrompt extends PromptElement {
-					render() {
-						return (
-							<>
-								<SystemMessage flexBasis={1} priority={2001}>
-									<TextChunk>
-										00 01 02 03 04 05 06 07 08 09
-										<br />
-										10 11 12 13 14 15 16 17 18 19
-										<br />
-									</TextChunk>
-								</SystemMessage>
-								<UserMessage flexBasis={1} priority={1000}>
-									<TextChunk priority={1000}>
-										HI HI 00 01 02 03 04 05 06 07 08 09
-										<br />
-										10 11 12 13 14 15 16 17 18 19
-										<br />
-									</TextChunk>
-									<TextChunk priority={500}>
-										HI MED 00 01 02 03 04 05 06 07 08 09
-										<br />
-										10 11 12 13 14 15 16 17 18 19
-										<br />
-									</TextChunk>
-									<TextChunk priority={100}>
-										HI LOW 00 01 02 03 04 05 06 07 08 09
-										<br />
-										10 11 12 13 14 15 16 17 18 19
-										<br />
-									</TextChunk>
-								</UserMessage>
-								<UserMessage flexBasis={1} priority={2000}>
-									<TextChunk priority={2000}>
-										LOW HI 00 01 02 03 04 05 06 07 08 09
-										<br />
-										10 11 12 13 14 15 16 17 18 19
-										<br />
-									</TextChunk>
-									<TextChunk priority={2000}>
-										LOW MED 00 01 02 03 04 05 06 07 08 09
-										<br />
-										10 11 12 13 14 15 16 17 18 19
-										<br />
-									</TextChunk>
-									<TextChunk priority={2000}>
-										LOW LOW 00 01 02 03 04 05 06 07 08 09
-										<br />
-										10 11 12 13 14 15 16 17 18 19
-										<br />
-									</TextChunk>
-								</UserMessage>
-							</>
-						);
-					}
-				}
-
-				const smallTokenBudgetEndpoint: any = {
-					modelMaxPromptTokens: 150 - BaseTokensPerCompletion,
-				} satisfies Partial<IChatEndpointInfo>;
-				const inst2 = new PromptRenderer(
-					smallTokenBudgetEndpoint,
-					TextChunkPrompt,
-					{},
-					tokenizer
-				);
-				const res2 = await inst2.render(undefined, undefined);
-				assert.equal(res2.messages.length, 2);
-				assert.equal(res2.messages[0].role, ChatRole.System);
-				assert.equal(res2.messages[1].role, ChatRole.User);
-				assert.equal(
-					res2.messages[1].content,
-					`LOW HI 00 01 02 03 04 05 06 07 08 09
-10 11 12 13 14 15 16 17 18 19
-
-LOW MED 00 01 02 03 04 05 06 07 08 09
-10 11 12 13 14 15 16 17 18 19
-`
-				);
-			});
-
-			test('are prioritized within prioritized lists', async () => {
-				class PriorityListPrompt extends PromptElement {
-					render() {
-						const textChunksA = [];
-						for (let i = 0; i < 100; i++) {
-							textChunksA.push(
-								<TextChunk>
-									{i.toString().padStart(3, '0')}
-								</TextChunk>
-							);
-						}
-
-						const textChunksB = [];
-						for (let i = 100; i < 200; i++) {
-							textChunksB.push(
-								<TextChunk>
-									{i.toString().padStart(3, '0')}
-								</TextChunk>
-							);
-						}
-
-						return (
-							<>
-								<SystemMessage>
-									Hello there, this is a system message.
-								</SystemMessage>
-								<UserMessage>
-									<PrioritizedList
-										priority={900}
-										descending={false}
-									>
-										{...textChunksA}
-									</PrioritizedList>
-									<PrioritizedList
-										priority={1001}
-										descending={false}
-									>
-										{...textChunksB}
-									</PrioritizedList>
-								</UserMessage>
-							</>
-						);
-					}
-				}
-
-				const smallTokenBudgetEndpoint: any = {
-					modelMaxPromptTokens: 150 - BaseTokensPerCompletion,
-				} satisfies Partial<IChatEndpointInfo>;
-				const inst2 = new PromptRenderer(
-					smallTokenBudgetEndpoint,
-					PriorityListPrompt,
-					{},
-					tokenizer
-				);
-				const res2 = await inst2.render(undefined, undefined);
-				assert.equal(res2.messages.length, 2);
-				assert.equal(res2.messages[0].role, ChatRole.System);
-				assert.equal(res2.messages[1].role, ChatRole.User);
-				assert.ok(
-					res2.messages[1].content.includes('199'),
-					'Higher-priority chunks from second user message were not included'
-				);
-				assert.ok(
-					!res2.messages[1].content.includes('099'),
-					'Lower-priority chunks from first user message were included'
-				);
-				assert.ok(
-					!res2.messages[1].content.includes('000'),
-					'Lower-priority chunks from first user message were included'
-				);
+				assert.equal(res2.tokenCount, 120 - BaseTokensPerCompletion);
 			});
 		}
 	);
@@ -1118,6 +1171,83 @@ LOW MED 00 01 02 03 04 05 06 07 08 09
 			);
 		});
 
+		test('does not emit empty messages', async () => {
+			const inst = new PromptRenderer(
+				fakeEndpoint,
+				class extends PromptElement {
+					render() {
+						return <>
+							<SystemMessage></SystemMessage>
+							<UserMessage>Hello!</UserMessage>
+						</>;
+					}
+				},
+				{},
+				new FakeTokenizer()
+			);
+			const res = await inst.render(undefined, undefined);
+			assert.deepStrictEqual(res.messages, [
+				{
+					role: 'user',
+					content: 'Hello!',
+				}
+			]);
+		});
+
+		test('does not add a line break in an embedded message', async () => {
+			class Inner extends PromptElement {
+				render() {
+					return <>world</>;
+				}
+			}
+			const inst = new PromptRenderer(
+				fakeEndpoint,
+				class extends PromptElement {
+					render() {
+						return <>
+							<UserMessage>Hello <Inner />!</UserMessage>
+						</>;
+					}
+				},
+				{},
+				new FakeTokenizer()
+			);
+			const res = await inst.render(undefined, undefined);
+			assert.deepStrictEqual(res.messages, [
+				{
+					role: 'user',
+					content: 'Hello world!',
+				}
+			]);
+		});
+
+		test('adds line break between two nested embedded messages', async () => {
+			class Inner extends PromptElement {
+				render() {
+					return <>world</>;
+				}
+			}
+			const inst = new PromptRenderer(
+				fakeEndpoint,
+				class extends PromptElement {
+					render() {
+						return <>
+							<UserMessage><Inner /><Inner /></UserMessage>
+						</>;
+					}
+				},
+				{},
+				new FakeTokenizer()
+			);
+			const res = await inst.render(undefined, undefined);
+			assert.deepStrictEqual(res.messages, [
+				{
+					role: 'user',
+					content: 'world\nworld',
+				}
+			]);
+		});
+
 		test('none-grow, greedy-grow, grow elements', async () => {
 
 			await flexTest(<>
@@ -1274,85 +1404,86 @@ LOW MED 00 01 02 03 04 05 06 07 08 09
 		});
 	});
 
-	suite('renderElementJSON', () => {
-		test('scopes priorities', async () => {
-			const json = await renderElementJSON(
-				class extends PromptElement {
-					render() {
-						return <>
-							<TextChunk priority={50}>hello50</TextChunk>
-							<TextChunk priority={60}>hello60</TextChunk>
-							<TextChunk priority={70}>hello70</TextChunk>
-							<TextChunk priority={80}>hello80</TextChunk>
-							<TextChunk priority={90}>hello90</TextChunk>
+	if (!process.env.IS_OUTSIDE_VSCODE) {
+		suite('renderElementJSON', () => {
+			test('scopes priorities', async () => {
+				const json = await renderElementJSON(
+					class extends PromptElement {
+						render() {
+							return <>
+								<TextChunk priority={50}>hello50</TextChunk>
+								<TextChunk priority={60}>hello60</TextChunk>
+								<TextChunk priority={70}>hello70</TextChunk>
+								<TextChunk priority={80}>hello80</TextChunk>
+								<TextChunk priority={90}>hello90</TextChunk>
+							</>;
+						}
+					},
+					{},
+					{ tokenBudget: 100, countTokens: t => Promise.resolve(tokenizer.tokenLength(t)) }
+				);
 
-						</>;
-					}
-				},
-				{},
-				{ tokenBudget: 100, countTokens: t => Promise.resolve(tokenizer.tokenLength(t)) }
-			);
+				const actual = await renderPrompt(
+					class extends PromptElement {
+						render() {
+							return <UserMessage>
+								<TextChunk priority={40}>outer40</TextChunk>
+								<ToolResult priority={50} data={{ [contentType]: json }} />
+								<TextChunk priority={60}>outer60</TextChunk>
+								<TextChunk priority={70}>outer70</TextChunk>
+								<TextChunk priority={80}>outer80</TextChunk>
+								<TextChunk priority={90}>outer90</TextChunk>
+							</UserMessage>
+						}
+					},
+					{}, { modelMaxPromptTokens: 20 }, tokenizer
+				);
 
-			const actual = await renderPrompt(
-				class extends PromptElement {
+				// if priorities were not scoped, we'd see hello80 here instead of outer70
+				assert.strictEqual(actual.messages[0].content, 'hello60\nhello70\nhello80\nhello90\nouter60\nouter70\nouter80\nouter90');
+			});
+
+			test('round trips messages', async () => {
+				class MyElement extends PromptElement {
 					render() {
-						return <UserMessage>
-							<TextChunk priority={40}>outer40</TextChunk>
-							<ToolResult priority={50} data={{ [contentType]: json }} />
-							<TextChunk priority={60}>outer60</TextChunk>
-							<TextChunk priority={70}>outer70</TextChunk>
-							<TextChunk priority={80}>outer80</TextChunk>
-							<TextChunk priority={90}>outer90</TextChunk>
-						</UserMessage>
+						return <>
+							Hello world!
+							<TextChunk priority={10}>
+								chunk1
+								<references value={[new PromptReference({ variableName: 'foo', value: undefined })]} />
+							</TextChunk>
+							<TextChunk priority={20}>chunk2</TextChunk>
+						</>;
 					}
-				},
-				{}, { modelMaxPromptTokens: 20 }, tokenizer
-			);
-
-			// if priorities were not scoped, we'd see hello80 here instead of outer70
-			assert.strictEqual(actual.messages[0].content, '\nhello90\nouter60\nouter70\nouter80\nouter90');
-		});
-
-		test('round trips messages', async () => {
-			class MyElement extends PromptElement {
-				render() {
-					return <>
-						Hello world!
-						<TextChunk priority={10}>
-							chunk1
-							<references value={[new PromptReference({ variableName: 'foo', value: undefined })]} />
-						</TextChunk>
-						<TextChunk priority={20}>chunk2</TextChunk>
-					</>;
-				}
-			}
-			const r = await renderElementJSON(
-				MyElement, {}, { tokenBudget: 100, countTokens: t => Promise.resolve(tokenizer.tokenLength(t)) }
-			);
-
-			const expected = await renderPrompt(class extends PromptElement {
-				render() {
-					return <UserMessage>
-						<MyElement />
-					</UserMessage>;
 				}
-			}, {}, fakeEndpoint, tokenizer);
+				const r = await renderElementJSON(
+					MyElement, {}, { tokenBudget: 100, countTokens: t => Promise.resolve(tokenizer.tokenLength(t)) }
+				);
 
-			const actual = await renderPrompt(
-				class extends PromptElement {
+				const expected = await renderPrompt(class extends PromptElement {
 					render() {
 						return <UserMessage>
-							<ToolResult data={{ [contentType]: r }} />
+							<MyElement />
 						</UserMessage>;
 					}
-				},
-				{}, fakeEndpoint, tokenizer
-			);
+				}, {}, fakeEndpoint, tokenizer);
+
+				const actual = await renderPrompt(
+					class extends PromptElement {
+						render() {
+							return <UserMessage>
+								<ToolResult data={{ [contentType]: r }} />
+							</UserMessage>;
+						}
+					},
+					{}, fakeEndpoint, tokenizer
+				);
 
-			assert.deepStrictEqual(actual.messages, expected.messages);
-			assert.deepStrictEqual(actual.references, expected.references);
+				assert.deepStrictEqual(actual.messages, expected.messages);
+				assert.deepStrictEqual(actual.references, expected.references);
+			});
 		});
-	});
+	}
 
 	test('correct ordering of child text chunks (#90)', async () => {
 		class Wrapper extends PromptElement {
@@ -1389,5 +1520,85 @@ LOW MED 00 01 02 03 04 05 06 07 08 09
 			'inafter',
 			'after',
 		].join('\n'));
-	})
+	});
+
+	suite('metadata', () => {
+		class MyMeta extends PromptMetadata {
+			constructor(public cool: boolean) {
+				super();
+			}
+		}
+
+		test('is extractable and global', async () => {
+			const res = await new PromptRenderer(
+				{ modelMaxPromptTokens: Number.MAX_SAFE_INTEGER } as any,
+				class extends PromptElement {
+					render() {
+						return <UserMessage>
+							Hello world!
+							<meta value={new MyMeta(true)} />
+						</UserMessage>;
+					}
+				},
+				{},
+				tokenizer
+			).render();
+
+			assert.deepStrictEqual(res.metadata.get(MyMeta), new MyMeta(true));
+		});
+
+		test('local survives when chunk survives', async () => {
+			const res = await new PromptRenderer(
+				{ modelMaxPromptTokens: Number.MAX_SAFE_INTEGER } as any,
+				class extends PromptElement {
+					render() {
+						return <UserMessage>
+							<TextChunk>Hello <meta value={new MyMeta(true)} local /></TextChunk>
+							<TextChunk>world!</TextChunk>
+						</UserMessage>;
+					}
+				},
+				{},
+				tokenizer
+			).render();
+
+			assert.deepStrictEqual(res.metadata.get(MyMeta), new MyMeta(true));
+		});
+
+		test('local is pruned when chunk is pruned', async () => {
+			const res = await new PromptRenderer(
+				{ modelMaxPromptTokens: 1 } as any,
+				class extends PromptElement {
+					render() {
+						return <UserMessage>
+							<TextChunk priority={1}>Hello <meta value={new MyMeta(true)} local /></TextChunk>
+							<TextChunk>world!</TextChunk>
+						</UserMessage>;
+					}
+				},
+				{},
+				tokenizer
+			).render();
+
+			assert.deepStrictEqual(res.metadata.get(MyMeta), undefined);
+		});
+
+		test('global survives when chunk is pruned', async () => {
+			const res = await new PromptRenderer(
+				{ modelMaxPromptTokens: 5 } as any,
+				class extends PromptElement {
+					render() {
+						return <UserMessage>
+							<TextChunk priority={1}>Hello <meta value={new MyMeta(true)} /></TextChunk>
+							<TextChunk>world!</TextChunk>
+						</UserMessage>;
+					}
+				},
+				{},
+				tokenizer
+			).render();
+
+			assert.deepStrictEqual(res.metadata.get(MyMeta), new MyMeta(true));
+		});
+	});
 });
diff --git a/src/base/tsx-globals.ts b/src/base/tsx-globals.ts
index 3e8bfb9..8409cf8 100644
--- a/src/base/tsx-globals.ts
+++ b/src/base/tsx-globals.ts
@@ -15,6 +15,11 @@ declare global {
 			 */
 			"meta": {
 				value: PromptMetadata;
+				/**
+				 * If set, the metadata will only be included in the rendered result
+				 * if the chunk it's in survives prioritization.
+				 */
+				local?: boolean;
 			};
 			/**
 			 * `\n` character.
diff --git a/src/base/types.ts b/src/base/types.ts
index eecba7a..81fa68a 100644
--- a/src/base/types.ts
+++ b/src/base/types.ts
@@ -83,7 +83,7 @@ export interface PromptElementCtor<P extends BasePromptElementProps, S> {
 }
 
 export interface RuntimePromptElementProps {
-	children?: PromptPiece[];
+	children?: PromptPieceChild[];
 }
 
 export type PromptElementProps<T> = T & BasePromptElementProps & RuntimePromptElementProps;