goxpath.go
func ParseExec(xpstr string, t tree.Node, opts ...FuncOpts) (tree.Result, error) {
	xp, err := Parse(xpstr)
	if err != nil {
		return nil, err
	}
	return xp.Exec(t, opts...)
}
func ParseExec(xpstr string, t tree.Node, opts ...FuncOpts) (tree.Result, error) {
	xp, err := Parse(xpstr)
	if err != nil {
		return nil, err
	}
	return xp.Exec(t, opts...)
}
//ParseExec parses the XPath string, xpstr, and runs Exec.