Document the $parse()$ inline function

streamerbot/2.guide/3.variables.md

@@ -173,6 +173,25 @@ $length(Lorem ipsum dolor sit amet consectetur adipisicing elit. Commodi, ut.)$
 $length(%rawInput%)$
 ```
 
+### `parse()`
+Fetches the value of the argument named by `parse`'s parameter, which itself can be the result of parsing variables. In other words, it lets you "double parse" a value. This is often useful in a [While](/api/sub-actions/core/logic/while) loop to access an array of numbered arguments with an index variable.
+
+```cs [Example]
+// Same results as %user%
+$parse(user)$
+
+// First, Set Argument %i% to 1
+$parse(line%i%)$
+// ==> returns value of %line1% (the first line of the file)
+
+// Set Argument %i% to $math(%i%+1)$ (i.e., 2)
+$parse(line%i%)$
+// ==> returns value of %line2% (the second line of the file)
+```
+::tip
+`%arguments%` and `~persistedVariables~` will be parsed in `parse`'s parameter, but not other `$inline()$` functions. If you wish to use a function, then set another argument to the output of the function, and use that argument in the `parse` instead.
+::
+
 ## Variable Viewer
 The Variable Viewer in Streamer.bot provides a convenient location to **view, modify, and create** all types of global variables, including per-platform user variables.