The command `(backspace)' toggles between <term to insert> and <term to insert>.

`(mouseleft)' on <term to insert> inserts the enclosed term at the slot, as specified in doc for term insertion.

`(mouseleft)' on <term to insert> is similar except that it reverses the left/right direction first. (See the `{(c-w)(m-w)(c-i)}' command.)

If you want to display the button as a mnemonic string, you should locate the point on the whole <term to insert> button and use the `(c-s)' command, which will convert the display, and then you should enter the display string you want.
If you use the empty string, say by hitting `(c-u){(tab)(return)}' on the text-slot prompt, the form will revert. You can also clear text with the `(c-a)(c-d)' command when the point is in the text. IF YOU CAN SEE THIS go to /sfa/Nuprl/Shared/Xindentation_hack_doc.html