# File TagTreeScanner.rb, line 416
                def insert_before( new_child, reference_child=nil )
                        return new_child if reference_child ? ( reference_child.previous_sibling == new_child ) : ( new_child == @child_tags.last )
                        insert_after( new_child, reference_child ? reference_child.previous_sibling : @child_tags.last )
                end