When I start AUCTeX there are no completions available for
reftex-citation. I have to give it a regular expression first and then
after selecting a citation it will be in the history for reftex-citation
and also I can tab-complete to it in the prompt for reftex-citation.
It seems like it would be easier to just tab out a citation key if I
know its beginning and have the citations completed from the
bibliography database instead of history. Is this possible?