diff --git a/Adding-a-new-operation.md b/Adding-a-new-operation.md
index 83c58e6..dd0bd32 100644
--- a/Adding-a-new-operation.md
+++ b/Adding-a-new-operation.md
@@ -64,6 +64,8 @@ Operation arguments (ingredients) can be set to any of the following types:
      - Operation receives an object with two properties: `option` containing the user's dropdown selection, and `string` containing the input box contents.
      - Particularly useful for arguments that can be specified in various different formats.
      - See the [XOR](https://github.com/gchq/CyberChef/blob/master/src/core/operations/XOR.mjs) operation for an example of how this works.
+ 10. `argSelector`
+     - `value` is an array of `name`, `on`, `off` triples. The user is presented with a dropdown selection box with each of the names as an option. `on` and `off` are arrays of argument numbers which are enabled/disabled when the corresponding option is selected. The ingredients are numbered according to their position in the `this.args[]` array. The name of the selected option is sent to the operation.
 
 **Ingredient Validation**