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Re: CIF specification: reserved prefixes

Hello Doug

> Probably misunderstandings on my part, but I had the impression that
> _data_name_tags had no semantic meaning of their own and parsing them is
> therefore against CIF philosophy. All the meaning is embedded in the
> associated dictionary definition for which there should be a precise string
> match.

Strictly, that's correct. Reserved prefixes simply guard against name
collisions by encouraging people to create tags with their own unique
prefix. I suppose my thoughts are running along the lines of specialist
applications (that maybe I'll get round to writing one day) that help
the registry to screen out candidate prefixes that would collide with existing
"official" category names - i.e. it would not be helpful if someone tried to
register "atom" as a private prefix.

> On the other hand, I thought that "." characters were synonymous with
> underscores in ddl2 and _ddl2_data.name_tags[] needed to be parsed and
> interpreted. So perhaps ".", "[" and "]" characters should also be banned
>  from prefixes in order not to trip up any software making such
>  philosophically corrupt interpretations?

"[" and "]" are not special, but are used by convention in a number of
cases. The convention makes it easier for a human reader to understand the
intent of a tag, but from the viewpoint of a machine parse they have no
significance. In DDL2 dictionaries "." is different: it rigorously separates
category from item. However, even so the DDL2 dictionary definitions specify
the category name, so arguably it's also a convention.

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