GtkTextTag tag, or to the next toggle of any tag if
tag is NULL. If no matching tag toggles are found,
returns FALSE, otherwise TRUE. Does not return toggles
located at iter, only toggles after iter. Sets iter to
the location of the toggle, or to the end of the buffer
if no toggle is found.gtkTextIterForwardToTagToggle(object, tag = NULL)objecttagGtkTextTag, or NULL. [ allow-none ]iter