If there is no selection, the caret and the mark are at the same location; otherwise the mark delimits the end-point of the selection opposite the caret.

editor-caret ( editor -- loc )

editor-mark ( editor -- loc )

change-caret ( editor quot: ( loc document -- newloc ) -- )

change-caret&mark ( editor quot: ( loc document -- newloc ) -- )

mark>caret ( editor -- )

Getting the selected text:

gadget-selection? ( gadget -- ? )

gadget-selection ( gadget -- string/f )

Removing selected text:

remove-selection ( editor -- )

Scrolling to the caret location:

scroll>caret ( editor -- )

Use user-input* to change selected text.