Imenu Documentation

[Tim Johnson]

I am looking at a website containing emacs documenations, specifically for the
usage of imenu:
http://www.club.cc.cmu.edu/pub/gnu/Manuals/elisp-manual-21-2.8/html_node/elisp_364.html#SEC364
(I find the same on my desktop)

There are some references that I do not fully understand.
Note the following lines:

"
Variable: imenu-generic-expression
  This variable, if non-nil, specifies regular expressions for finding
  definitions for Imenu. In the simplest case, elements should look like this:

  (menu-title regexp subexp)
"

Now note the following a few lines following the quotation above:

"
For Emacs Lisp mode, pattern could look like this:
[complex regular expression follows....]

"

Now, here is where I am confused: 

The word 'pattern' has no prior reference. Does the author mean that the
'pattern' refers to the word 'regexp'  in the form:

(menu-title regexp subexp)
??? 

Perhaps someone could help to clarify this matter?

Any further pointers to documenation on imenu would be appreciated.

Thanks
-- 
Tim Johnson <tim@johnsons-web.com>
      http://www.alaska-internet-solutions.com