undocumented? struggled with category filter on daily/weekly agenda view custom command.

[Brady Trainor <algebrat@uw.edu>]

Goal: To make an agenda view custom command that will filter a daily/weekly
view by category. 


I tried to use the documented `org-agenda-category-filter-preset', similar
to functionality of the analogous tag variable,
`org-agenda-tag-filter-preset'. It does not seem to work. However, a word
search in the `org-agenda.el' file uncovered an undocumented variable
`org-agenda-category-filter', which seemed to do the job for me. 

(That is, `C-h v' on the latter leads to "Not documented as a variable.") 

Am I using the right variable for the job? I do not really understand the
"preset" nomenclature. Does this mean it should only be used on the global
block, as opposed to say inside of `(agenda "" ...)'? 



Here are some minimal examples I used to work out where my issue was: 

 ____
/

(setq 
 org-agenda-custom-commands 
 '(("r" 
    "the real test" (
                     (agenda "")
                     (todo "")
                                ;; +CATEGORY=\"acat\"
                     )(
                       (org-agenda-files
'("/e/emacs-config/therealagendatest.org"))
                       ;; (org-agenda-filter-preset '("+acat"))
                       (org-agenda-category-filter '("+acat"))
                       ))))

\____
/

* TODO an appt
<2014-04-15 Tue>
* TODO a test todo                                                     :acat:
:PROPERTIES:
:CATEGORY: acat
:END:

\____


- Brady