This option allows you to add a custom callback function for execCommand handling. This enables you to override internal command functions in TinyMCE. The example below shows how the mceLink and mceImage are overridden.

Use the addCommand method instead.

Example of usage of the execcommand_callback option:

function myCustomExecCommandHandler(editor_id, elm, command, user_interface, value) {
	var linkElm, imageElm, inst;

	switch (command) {
		case "mceLink":
			inst = tinyMCE.getInstanceById(editor_id);
			linkElm = tinyMCE.getParentElement(inst.selection.getFocusElement(), "a");

			if (linkElm)
				alert("Link dialog has been overriden. Found link href: " + tinyMCE.getAttrib(linkElm, "href"));
			else
				alert("Link dialog has been overriden.");

			return true;

		case "mceImage":
			inst = tinyMCE.getInstanceById(editor_id);
			imageElm = tinyMCE.getParentElement(inst.selection.getFocusElement(), "img");

			if (imageElm)
				alert("Image dialog has been overriden. Found image src: " + tinyMCE.getAttrib(imageElm, "src"));
			else
				alert("Image dialog has been overriden.");

			return true;
	}

	return false; // Pass to next handler in chain
}

tinyMCE.init({
	...
	execcommand_callback : "myCustomExecCommandHandler"
});

An additional note: if you have URL processing rules, you may wish to apply these to the HREF of the attribute you're using, as follows (getFocusElement should be replaced by getNode in 3.xx):

	var linkRef = (linkElm) ? tinyMCE.getAttrib(linkElm, "href") : '';
	if (linkRef != '')
		linkRef = tinyMCE.convertURL(linkRef, inst.selection.getFocusElement(), false);