goxpath.go
func Parse(xp string) (XPathExec, error) {
	n, err := parser.Parse(xp)
	return XPathExec{n: n}, err
}
func Parse(xp string) (XPathExec, error) {
	n, err := parser.Parse(xp)
	return XPathExec{n: n}, err
}
//Parse parses the XPath expression, xp, returning an XPath executor.