gtk:editable-delete-text (editable &key start end)

editable -- a gtk:editable widget
start -- an integer for the start position, the default value is 0
end -- an integer for the end position, the default value is -1

Deletes a sequence of characters. The characters that are deleted are those characters at positions from start up to, but not including end. If end is negative, then the characters deleted are those from start to the end of the text. Note that positions are specified in characters, not bytes.