class Magick::RVG::Text

def tref(obj, x = nil, y = nil)

like x and y in RVG::TextBase#tspan
Reference a Tspan object. x and y are just 
def tref(obj, x = nil, y = nil)
  raise ArgumentError, "wrong argument type #{obj.class} (expected Tspan)" unless obj.is_a?(Tspan)
  obj = obj.deep_copy
  obj.parent = self
  tref = Tref.new(obj, x, y, self)
  @tspans << tref
  tref
end