You are looking at documentation for an older release. Not what you want? See the current release documentation.
If you execute an XPath request like this:
XPath
// get QueryManager
QueryManager queryManager = workspace.getQueryManager();
// make XPath query
Query query = queryManager.createQuery("/jcr:root/Documents/Publie/2010//element(*, exo:article)", Query.XPATH);
You will have an error: "Invalid request". This happens because XML does not allow names starting with a number - and XPath is part of XML: http://www.w3.org/TR/REC-xml/#NT-Name
Therefore, you cannot do XPath requests using a node name that starts with a number.
Easy workarounds:
Use an SQL request.
Use escaping.