set_selection
Entity: predicate

Usage:
get_selection(Edit, From, To)
set_selection(Edit, From, To)

Gets/Sets the selected text into an edit box

From     the starting position of the selected text
To         the ending position of the selected text
 

Examples:
?-
  ...
  set_selection(Edit, 10, 35),
  get_selection(Edit, From, To),