class Magick::RVG::Text

def tref(obj, x=nil, y=nil)
    unless obj.is_a?(Tspan)
        fail ArgumentError, "wrong argument type #{obj.class} (expected Tspan)"
    end
    obj = obj.deep_copy
    obj.parent = self
    tref = Tref.new(obj, x, y, self)
    @tspans << tref
    tref
end