Komodo is a good way to browse the php code, and functions in particular.

Then when you click on function, you can view the comments for that function. Notice the search form, typing in part of the function name will filter the window to only show functions which contain the search text. Here I typed 'cache'...

Also double clicking on a function in the view on the left of Komodo will make the text editor part on the right jump to that function definition.