Behat forms steps very slow

The behat form field manager is very slow, in particular in get_field_node_type which takes a NodeElement and tries to determine the type of field base do various attributes. It does this by asking the NodeElement for things like tagname, attributes, class, etc.

Unfortunately this is very slow because the Mink NodeElement requests that information from WebDriver. On a large page containing lots of detail, this is very slow!!

This is a quick attempt to use DOMDocument, DOMNode, and DOMXPath locally instead.