Global section in CIF headers

[Joe Krahn]

I have been thinking that it makes sense to allow a global_ block as 
part of a CIF file. Globals have been excluded because they don't fit 
very well into the data model, but it might be useful to allow them to 
provide general format hints to the parser.

My idea is that a common low-level parser could be used for mmCIF, CIF, 
and possibly other STAR variants. The global_ header would define 
parsing rules for the file, including possible future revisions of the 
same format, but not be considered part of the actual mmCIF data. For 
example:

global_
_format         mmCIF
_version        1.2

In a way, this just replaces the initial comment-embedded CIF 
identifier, but I have always dislike the idea of a comment containing 
data. This approach could be more detailed, depending on how much the 
CIF/mmCIF format changes over time. Will it ever include STAR 2.0 
bracketed lists? Will they ever directly include Unicode text?

Joe Krahn