[ddlm-group] FYI: CIF2 table keys are unique

This is essentially an FYI regarding the CIF2 syntax standard.

While I believe the uniqueness of keys within a CIF2 table is implicit in the language used in the STAR2 paper (table keys are used to 'index' data values), it has never been explicitly stated to my knowledge, so the explicit statement could be interpreted as an update to the standard. Therefore, this email is just to let you know that the CIF2 syntax chapter in the next edition of Volume G will explicitly state that table keys are unique within their table, unless there are objections from this group.

As CIF2 tables are used only in dictionaries so far, and they all meet this criterion, there is no practical effect from making this stipulation.
--