So you've run up against an empty page in the WordPress Codex's Function Reference. Where do you turn? Here are some sites that may help you in your search for answers.

1. Where
the
Codex
Ends

2. The WordPress Codex

4. The Question

5. Google time

6. How about that?

7. Uh oh.

8. Now what?

9. There are other worlds than these.
^sites

10. Adam Brown's WP Hook Database

12. WP Hooks over time

13. wpseek.com

14. wpseek.com - autocomplete

15. Ah, there it is.

16. Detail view

17. Function in situ
...hmm, apply_filters( 'upload_size_limit'... ),
eh?

18. Let's check out that filter...

19. Not much there.

20. Or in the Codex.

21. Guess it's time to check
the code on Trac.

22. Trac URLs

23. 3.6.1 code

24. Armed with that info...

25. And the followup

26. What it was

27. QueryPosts.com

31. Improving the Codex
Because the Codex is a community-edited wiki,
anyone with a WordPress.org ID can add pages
to the Codex. So, once I have a clear idea how
wp_max_upload_size() works, I can add that
info to the Codex. (I haven't yet. But I should.)

32. References &c
● Photos (CC-licensed):
– “This is where the sidewalk ends...” by Marissa Garza
http://www.flickr.com/photos/marzbars/3688823218/
– “Mark Cries in the Fetal Position” by Jared Cherup
http://www.flickr.com/photos/jarbo/2612243/
● http://wordpress.stackexchange.com/
● http://wpseek.com/
● http://queryposts.com/
● And of course http://codex.wordpress.org/

33. Thanks!