Hello,

I've attached a patch for the Advanced configuration (for exporting)
chapter of the Org mode manual that extends the hook example there to
provide the commonly requested ignoreheading-like functionality found in
the Beamer backend. The example is very simple and adds just one line of
code to the function thanks to the MATCH argument of the `org-map-entries`
function.
The commit message contains the TINYCOMMIT cookie as I'm not a FSF member.

Originally I only intended this solution to be an answer to questions on
StackOverflow that did not help me much (
http://stackoverflow.com/a/29588450/4779220), but I think it is something
very commonly requested and should be documented and easily accessible.

How I discovered this solution:
I've always liked the `ignoreheading` tag functionality in Beamer export. I
wanted to have something like it for all export backends.
The solutions I found on the Internet either didn't work or were filter
based which did not remove the headline nodes in the parsed structure.
So I decided to make my own solution. I found the hook example for removing
all headlines before processing in the Org manual. That was almost what I
wanted, but I needed to limit it to headlines with a tag. I had a look at
the documentation of the `org-map-entries` function and discovered the
MATCH argument that can match tags like in agenda views. So in the end I
added just 1 line of code to the example.

This experience once again showed me that Emacs truly is an extensible
self-documenting editor. I'd like to express my gratitude to all the
contributors of Emacs and Org mode.

Kind regards,
Ondřej Grover