Where do those magical commands come from (app.commands.execute)?

When reading codes about jupyterlab extensions, I often see some powerful commands like app.commands.execute(‘docmanager:open’) , app.commands.execute(‘docmanager:new-untitled’) . I wonder where do those strings(like ‘docmanager:new-untitled’) come from? What’s the detailed process behind them ? There must be more useful commands like this, I just don’t know how to find them.

These are application-level lumino commands and are covered by a number of documentation sources:

Some full examples: