Toggle macro

[tim89531]

I have the following macro which adds the string “\” (two slashes) to the end of each line in a selection.

[code]

 {
      "args":
      {
         "to": "line"
      },
      "command": "expand_selection"
   },
   {
      "args": null,
      "command": "split_selection_into_lines"
   },
{
	"args":
	{
		"by": "characters",
		"forward": true
	},
	"command": "move"
},
{
	"args":
	{
		"characters": "\\\\"
	},
	"command": "insert"
}

][/code]

Now my question: How can I change this into a toggle-style macro?
i.e. remove the double-slash at the end of each line in the selection if it is present, but add the double slash if it is not present.
This is a very similar idea to the toggle comment menu item.
I tried to locate this menu item to inspect the code but I could not find it.