Scripts extending this class and implementing its [code]_run()[/code] method can be executed from the Script Editor's [code]File -> Run[/code] menu option (or by pressing [code]CTRL+Shift+X[/code]) while the editor is running. This is useful for adding custom in-editor functionality to Godot. For more complex additions, consider using [EditorPlugin]s instead. Note that extending scripts need to have [code]tool mode[/code] enabled.
Note that the script is run in the Editor context, which means the output is visible in the console window started with the Editor (STDOUT) instead of the usual Godot *Output* dock.