Limit cleanup() calls to once per scope

docs/api/reactivity-utility.md

@@ -2,7 +2,7 @@
 
 ## cleanup()
 
-Runs a callback anytime a reactive scope is re-ran.
+Runs a callback anytime a function scope is re-ran.
 
 - **Type**
 
@@ -10,6 +10,19 @@ Runs a callback anytime a reactive scope is re-ran.
     function cleanup(callback: () -> ())
     ```
 
+- **Details**
+
+    The primary purpose of this function is to provide a means of cleaning up
+    side effects caused by source updates and `watch()` updates.
+
+    The stack is inspected to find the function that calls `cleanup()`. The
+    callback passed is called anytime the caller is re-ran, and when the caller
+    finally garbage collects.
+
+    ::: warning
+    Only one `cleanup()` call is allowed per function scope.
+    :::
+
 - **Example**
 
     ```lua

docs/api/strict-mode.md

@@ -17,6 +17,7 @@ Currently, strict mode will:
 4. Checks for `indexes()` and `values()` returning primitive values.
 5. Checks for duplicate nested properties at same depth.
 6. Better error reporting and stack traces.
+7. Checks for multiple `cleanup()` calls in the same function scope.
 
 By rerunning sources and watchers, any side-effects are made more apparent.
 This also helps ensure that cleanups are being handled correctly.