gtk:editable-selection-bounds (editable)

editable -- a gtk:editable widget

start -- an integer with the starting position, or nil
end -- an integer with the end position, or nil

Retrieves the selection bound of the editable. The start value will be filled with the start of the selection and the end value with end. If no text was selected both will be identical and nil will be returned.

Note that positions are specified in characters, not bytes.