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Re: [ddlm-group] THREAD 3: The alphabet of non-delimited strings.

Dear All:

As a result of the discussion with Herbert I can see two differing
approaches to these CIF syntax changes:

1. Any changes to CIF syntax should be such that earlier syntax
versions form a subset of the new syntax, i.e. files in the older
syntax will also conform to the new syntax

or

2. When making changes to the standard, the opportunity should be
taken to simplify and streamline syntax as much as possible.

Advantages of (1): a single CIF parser can be maintained for all
syntax versions; a CIF writer is always conformant to the latest
version and only needs changing if new syntax features are to be used;
the existing CIF software ecosystem is minimally affected

Advantages of (2): implementation of CIF readers/writers from scratch
is easier; the standard is easier to define formally and more
aesthetically pleasing; mistakes in previous versions can be fixed,
warts do not accumulate

I would like to suggest we act as follows: in essence, we deprecate
rather than exclude.  In detail:

1. For this edition of the standard (1.2) we follow Herbert's line,
leaving everything currently defined untouched.  We simply add triple
quote delimited strings and bracket expressions.  The content of
non-delimited strings in bracket expressions will be as proposed by
Nick.

2. In the documents associated with the new standard we strongly
suggest that all non-delimited strings use the same character set as
for non-delimited strings in bracket expressions (i.e. Nick's original
proposal).  We might point out that this simplifies code for writing
CIFs, and perhaps (if all agree) we add that using the CIF1.1
non-delimited string character set is deprecated, darkly foreshadowing
that a future version of the syntax standard will adopt this character
set for all non-delimited strings.

3. We also deprecate including string delimiters inside strings,
regardless of whitespace issues.

4. In all dictionaries we adopt the restricted character set for
non-delimited strings and exclusion of string delimiters in strings.

5. We ask that CheckCIF emit a warning about use of deprecated
characters in non-delimited strings

6. When (say in 10 years' time) a sufficiently large proportion of
incoming CIFs conform to the new non-delimited string character set,
we promulgate the 1.3 version of the standard.


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