website: add mark decoration example.

www/src/pages/examples/MarkDecoration.tsx

@@ -0,0 +1,84 @@
+import CodeMirror, { ReactCodeMirrorRef } from '@uiw/react-codemirror';
+import { useRef } from 'react';
+
+import { Decoration, drawSelection, EditorView, lineNumbers, ViewPlugin, WidgetType } from '@codemirror/view';
+
+class SimpleWidget extends WidgetType {
+  toDOM() {
+    const element = document.createElement('span');
+    element.className = 'filler';
+    return element;
+  }
+}
+
+const extensions = [
+  lineNumbers(),
+  drawSelection(),
+  ViewPlugin.define(
+    () => {
+      return {
+        decorations: Decoration.set([
+          Decoration.widget({
+            widget: new SimpleWidget(),
+            side: 1, // is after the cursor
+          }).range(34),
+
+          Decoration.mark({
+            class: 'wrapper',
+          }).range(60, 70),
+
+          Decoration.widget({
+            widget: new SimpleWidget(),
+            side: 1, // should be after the cursor
+          }).range(67),
+        ]),
+      };
+    },
+    {
+      decorations: (value) => value.decorations,
+    },
+  ),
+  EditorView.baseTheme({
+    '.filler': {
+      display: 'inline-block',
+      width: '8px',
+      height: '1em',
+      backgroundColor: '#9c9',
+    },
+    '.wrapper': {
+      border: '1px solid #aaa',
+    },
+  }),
+];
+
+const code = `The cursor is before this widget:
+
+The cursor is after this widget
+dsddfsdfsdfdf
+Is this how it should work?`;
+
+export function Component() {
+  let $edit = useRef<ReactCodeMirrorRef | null>(null);
+  function refCallack(editor: ReactCodeMirrorRef) {
+    if (!$edit.current && editor?.editor && editor?.state && editor?.view) {
+      // first time we got ref, similar to useEffect
+      console.log(editor); // do something with editor
+      $edit.current = editor; // store it
+    }
+  }
+  return (
+    <div>
+      <CodeMirror
+        value={code}
+        theme="none"
+        ref={refCallack}
+        height="400px"
+        width="100%"
+        style={{ margin: '0 0 23px 0', flex: 1 }}
+        extensions={[extensions]}
+      />
+    </div>
+  );
+}
+
+Component.displayName = 'HomePage';

www/src/router.tsx

@@ -547,6 +547,11 @@ export const routes: MenuRouteObject[] = [
             label: 'Refs Example',
             lazy: () => import('./pages/examples/ExampleRef'),
           },
+          {
+            path: 'mark-decoration',
+            label: 'Mark Decoration Example',
+            lazy: () => import('./pages/examples/MarkDecoration'),
+          },
         ],
       },
     ],