Hi Martin,
The om.DomNode.selectByPath has a limited syntax so as to support its intended use for finding nodes in the DOM tree. So as per the documentation ...
http://4js.com/online_documentation/fjs-fgl-manual-html/#c_fgl_ClassDomNode_selectByPath.html ...and the example ...
http://4js.com/online_documentation/fjs-fgl-manual-html/#c_fgl_ClassNodeList_example_2.html you just need to modify your clause to match what is given there.
Something like (hopefully the slashes and quotes make it through to what you read)
domtree.selectByPath("//*[@name=\"page_tab\"]")
Historically I've wrapped it in a library function so I don't have to deal with the slashes and quotes each time when I call it!
Reuben