Placing the cursor over the User-defined Tools command rolls out a sub-menu containing custom-made commands that use external applications. In the screenshot below, two custom commands: (i) to open the parent folder in Windows Explorer, and (ii) to open the active file in Altova XMLSpy. You can create these commands in the Tools tab of the Customize dialog. Clicking one of these custom commands executes the action associated with this command.
Below the listing of custom commands that you have created, is the Customize command (see screenshot). This opens the Tools tab of the Customize dialog, enabling you to go directly to the dialog in which you can edit an existing custom command or create a new custom command.