Model component for format element. This element defines conversion to
and from simple unstructured text representations.
author: Dennis M. Sosnoski version: 1.0
Prevalidate attributes of element in isolation. Note that this adds the
format information to the context, which is necessary because the string
attributes for values need to have access to the format information for
their own prevalidation. This is the only type of registration which is
done during the prevalidation pass.
Parameters: vctx - validation context