[AUCTeX] reftex-citation to complete from all citations instead of just ones used previously?

[Michael Hoffman]

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?

Michael Hoffman