[O] org-tag-alist and org-tag-persistent-alist

[giovanni bono]

hello,

i would appreciate help in understanding the difference between
`org-tag-alist' and `org-tag-persistent-alist'.

the docstrings suggest that the first defines "allowed" tags, while the
second is for "always present" tags.  the info seems to mention both
only wrt completing tags for interactive insertion.  they sure behave
differently.  i am keeping a lot of files in `org-agenda-files' --more
than 100-- and i am using many tags.  while harvesting tags to clean
them up, for some reason i switched from the the persistent to the non
persistent alist variable.  as a result, `org-agenda-list' failed to
terminate in ten minutes, as opposed to the usual 2 seconds.  going back
to the persistent alist variable fixes the problem.  this looks strange
also because there is a `org-tag-alist-for-agenda'.

i am not sure whether this warrants submitting a bug.  my unfounded
guess is that `org-tag-alist' is there to pave the way for a facility to
keep tags growth in check --by signaling where one used non allowed
tags, for instance.  by the way, that would be very nice.  another
somewhat baseless guess is that `org-global-tags-completion-table' might
be causing the problem, as it uses two nested mapcar over agenda files
and `org-tag-alist'.

thanks,

  giovanni