QVT — OCL extensions

I've started writing a QVTr parser. So far it just does syntax analysis.
It highlights a number of significant issues in the grammar and enables
many mistakes to be removed from the Relations to Core example.

OCL extension
-------------

7.13 should enumerate the new keywords:
checkonly
domain
enforce
extends
implementedBy
import
key
overrides
primitive
query
relation
top
transformation
when
where
and stress that they are not reserved words and so may appear in identifier. At least I presume this is the intent, since 'domain'
is used in the Relation To Core example. I'm not entirely sure that a domain called OclAny is unambiguous, and is one called self
useful?

The OCL and consequently the QVT syntax lack formality here.
OCL extensions

Insert a new sub-section named "Keywords" in 7.13 to list the keywords. This section is to be inserted before the "Relations textual Syntax Grammar" sub-section. The text of the section will be as follows:

Keywords:
checkonly, domain, enforce, extends, implementedby, import, key, overrides
primitive, query, relation, top, transformation, when, where.

All these keywords are reserved words, they cannot be used as identifiers.
The "_" OCL prefix convention for escaping reserved words can be used to refer to conflicting properties or class names.