class REXML::Parsers::XPathParser

def UnionExpr path, parsed
  n = []
  rest = PathExpr( path, n )
  if rest != path
    while rest =~ /^\s*(\|)\s*/
      n = [ :union, n, [] ]
      rest = PathExpr( $', n[-1] )
    end
  end
  if parsed.size == 0 and n.size != 0
    parsed.replace( n )
  elsif n.size > 0
    parsed << n
  end
  rest
end