To stash a section of your script, first select it by highlighting it, then click the stash icon in the palette bar at the bottom of the window. You can also use the keyboard shortcuts option+delete (on a mac) or alt+backspace (on a pc). The highlighted portion of your script will appear in the Stash in your right sidebar.
To return the stashed section to your script, simply drag it from the stash and drop it where you want it to go.
