def initialize(parent)
unless parent.kind_of?(TkCanvas)
fail ArguemntError, "expect TkCanvas for 1st argument"
end
@c = parent
@cpath = parent.path
@path = @id = 'current'
CTagID_TBL[@cpath] = {} unless CTagID_TBL[@cpath]
CTagID_TBL[@cpath][@id] = self
end