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[ddlm-group] Revisiting list delimiters

Dear DDLm-group,

In the process of preparing for a vote on accepting the DDLm
dictionary, I have come to the conclusion that we need to revisit the
question of the separator character for lists.  This is because the
only fully-functional software for processing DDLm domain dictionaries
(Nick, Syd and Ian's demonstration software) expects a comma
separator, and my understanding is that Syd and Nick (now) are
strongly in favour of sticking with comma as the list separator for
STAR2.  Furthermore, other non-CIF domains collaborating with Nick and
Syd are already using comma as a list separator in STAR2 data files.
Additionally, I've formed the view that a comma is a useful visual aid for
distinguishing looped items and listed items.

I've reviewed our previous discussion starting at message:
http://www.iucr.org/__data/iucr/lists/ddlm-group/msg00338.html and
culminating in a tally at
http://www.iucr.org/__data/iucr/lists/ddlm-group/msg00406.html (with a
late vote after this from John W. for spaces only).  It seems that the
strongest preferences expressed were from Herb (for comma and space)
and from John W (for space only in order to avoid mixed-delimiter
strings).

I would therefore like to propose that we switch to allowing comma
*or* space as list item delimiters.  This will considerably simplify
the work needed to adapt the current DDLm/dREL software and
documentation.  I am also open to switching back to comma only, but think
that that might meet with some resistance.

I apologise for reopening this old discussion, but it looks like
reintroducing commas will produce the best practical outcome.  Note
that I would propose keeping the behaviour that was generally accepted
in the previous discussion, i.e.

* two commas without an intervening value is a syntax error, as is a
trailing comma
* lists may use a combination of comma and whitespace separation
(although one might expect that to be vanishingly rare in practice)
but this should be discouraged.

If I hear no strong dissenting voices, I will produce some draft text
for your comment
then edit it into the draft standard when it next comes before COMCIFS.

Once we have resolved this issue, I will edit the draft DDL
specification to take into
account variations in CIF2 syntax from that assumed for the original
specification, then
present it for your vote.

James.
-- 
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