XMI12 — Multi-valued Attributes in the simple DTD ruleset

The EBNF (4d, 4f) and pseudo-code for Attribute contents in the simple
DTD ruleset seem to support multi-valued Attributes in different ways.
In the EBNF, "attribute contents" have an enclosing "( )*" in the two
cases that matter. By contrast, in the pseudo-code, the "( )*" 's are
sometimes present and sometimes absent.

I think the EBNF is probably correct.

There are also some minor meta-syntax errors in the pseudo-code;
e.g. missing quotes.

Removal of obsolete OCL and pseudo-code