Moves @iter to the start of the previous line. Returns %TRUE if
@iter could be moved; i.e. if @iter was at character offset 0, this
function returns %FALSE. Therefore if @iter was already on line 0,
but not at the start of the line, @iter is snapped to the start of
the line and the function returns %TRUE. (Note that this implies that
in a loop calling this function, the line number may not change on
every iteration, if your first iteration is on line 0.)
Moves @iter to the start of the previous line. Returns %TRUE if @iter could be moved; i.e. if @iter was at character offset 0, this function returns %FALSE. Therefore if @iter was already on line 0, but not at the start of the line, @iter is snapped to the start of the line and the function returns %TRUE. (Note that this implies that in a loop calling this function, the line number may not change on every iteration, if your first iteration is on line 0.)
Return: whether @iter moved