Error location and fragment parsing

There are some special considerations when fragment parsing is enabled:

If the fragment context denotes that the fragment is an attribute value, then the error location will be a zero length string.
If the error occurs before or after the main element in the fragment, the error location will be a zero length string.
The XEH_ErrFlags field can only have the XEH_ERRXMLDECL bit on if the error occurs in the text declaration portion of the fragment, or the XEH_ERRELEMENT bit on if it occurs anywhere else in the fragment.