# File lib/ruote/exp/ro_variables.rb, line 182
    def locate_var (var, prefix=nil)

      var, prefix = split_prefix(var, prefix)

      return nil if prefix.length >= 2 # engine variable
      return parent.locate_var(var, prefix) if prefix.length == 1 && h.parent_id

      # no prefix...

      return [ self, var ] if h.variables
      return parent.locate_var(var, prefix) if h.parent_id

      raise "uprooted var lookup, something went wrong"
    end