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

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

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