Add documentation

docs/src/configuration.md

@@ -248,6 +248,50 @@ Eww then reads the provided value and renders the resulting widget. Whenever it
 
 Note that this is not all that efficient. Make sure to only use `literal` when necessary!
 
+## Dynamically generated windows with arguments and ids
+
+In some cases you may want to use the same window configuration for multiple widgets, e.g. for multiple windows. This is where arugments and ids come in.
+
+Firstly let us start off with ids. An id can be specified in the `open` command with `--id`, by default the id will be set to the name of the window configuration. These ids allow you to spawn multiple of the same windows. So for example you can do:
+
+```bash
+eww open my_bar --screen 0 --id primary
+eww open my_bar --screen 1 --id secondary
+```
+
+However you may want to have slight changes for each of these bars, e.g. spawning other windows on the same monitor. This is where the arguments come in.
+
+Defining arguments in a window is the exact same as in a widget so you can have:
+
+```lisp
+(defwindow my_bar [arg1 ?arg2]
+          :geometry (geometry
+                       :x      "0%"
+                       :y      "6px"
+                       :width  "100%"
+                       :height "30px"
+                       :anchor "top center")
+          :stacking   "bg"
+          :windowtype "dock"
+          :reserve    (struts :distance "50px" :side "top")
+    ...)
+```
+
+Here we have two arguments, `arg1` and `arg2` (an optional parameter).
+
+Once we have these parameters, when opening a new window, we must specify them (unless they are required, like `arg2`), but how? Well, we use the `--args` option when running the `open` command:
+
+```bash
+eww open my_bar --id primary --args arg1=some_value,arg2=another_value
+```
+
+You may notice that this is the same layout to set values with `update` and you'd be correct.
+
+So, now you know the basics, I shall introduce you to some of these "special" parameters, which are set slightly differently. However these can all be overridden by the `--args` option.
+
+- `id` - If `id` is included in the argument list, it will be set to the id specified by `--id` or will be set to the name of the config. This can be used when closing the current window through eww commands.
+- `screen` - If `screen` is specified it will be set to the value given by `--screen`, so you can use this in other widgets to access screen specific information.
+
 ## Generating a list of widgets from JSON using `for`
 
 If you want to display a list of values, you can use the `for`-Element to fill a container with a list of elements generated from a JSON-array.