The expression /bookstore/book[1]/title
should return <title lang="eng">Harry Potter</title>
but instead I get "The regular expression does not match..."
Here is my XML that I am testing:
<?xml version="1.0" encoding="ISO-8859-1"?>
<bookstore>
<book>
<title lang="eng">Harry Potter</title>
<price>29.99</price>
</book>
<book>
<title lang="eng">Learning XML</title>
<price>39.95</price>
</book>
</bookstore>
While RB can handle regular expressions for XPath, but it doesn't handle XPath paths. For constructing/checking what's selected etc of XPath paths you'd need something like XPath Explorer, Firefox with Firebug+Firepath, or similar.