[Orgmode] Custom filtering the agenda by (file) tag

[Rick Moynihan]

Hi all,

I've been setting up a whole bunch of org-agenda-custom-commands and
am having trouble setting up a filter to display ONLY items in the
agenda view which are tagged PERSONAL across all my org-agenda-files.

I tried several ways to do this and ended up trying the following:

(org-add-agenda-custom-command
 '("b" agenda "Personal Agenda"
   ((org-agenda-skip-function '(org-agenda-skip-subtree-if
                                'notregexp ":PERSONAL:")))))

Unfortunately this doesn't appear to work with FILETAGS as it relies
on matching against a regex.  How can I implement this view with full
tag support and inheritance?

Thanks again,

R.