Encoding Values in DOMXPath Query Expressions

What is the best way to "encode" values passed to XPath expressions to 
ensure that they work correctly?

For example, in the code below, what should I do to $value before 
incorporating it in the expression?

htmlentities(), htmlspecialchars(), what?

$query = "//book/chapter[name='$value']";

$xPath = new DOMXPath($domDoc);
$nodeList = $xPath->query($query);

Thanks in Advance for any help given.