docs(reference): clarify platform and workspace behavior for variables (#9191)

* docs(reference): add platform and workspace considerations for variables

* Revise variables reference for clarity and consistency

Updated section titles and improved clarity of platform-specific behavior and workspace context.

Author: DakotaB75

docs/reference/variables-reference.md

@@ -64,6 +64,18 @@ This leads to the following values for each of the variables:
 > [!TIP]
 > Use IntelliSense inside string values for `tasks.json` and `launch.json` to get a full list of predefined variables.
 
+## Platform and workspace considerations
+
+### Platform-specific behavior
+
+Some predefined variables may resolve differently depending on the operating system:
+
+- On **Windows**, file paths use backslashes (`\`). When composing paths in JSON files such as `tasks.json` or `launch.json`, ensure backslashes are properly escaped (for example: `"${workspaceFolder}\\subdir"`).
+- On **macOS** and **Linux**, file paths use forward slashes (`/`).
+
+It's recommended to use `${pathSeparator}` or `${/}` to make configurations portable across platforms.
+
+
 ### Variables scoped per workspace folder
 
 By appending the root folder's name to a variable (separated by a colon), it is possible to reach into sibling root folders of a workspace. Without the root folder name, the variable is scoped to the same folder where it is used.