TBH, I'd have spent more time documenting the excel file if it wasn't for the fact that:

a) the current excel export doesn't actually work for me( and some users also report this ) as it generates an excel file that seems to play up in newer versions of excel/windows - this may depend on what other applications are installed of course.

b) I'd previously wrote a patch to drop this file and replace with DOCX/XLSX i.e. actually excel generation files.

So it seemed it would be a waste of time to spend longer documenting these new bits to the excel api whilst also proposing to nuke the file in a file days. Of course, if we do decide to keep, it'll be worth re-iterating back over this to add better long term comments. 

My hope is once we've got phpdoc comments embedded in properly, we'll ensure we never 'error' the documentation when adding code changes, and that instead, it'll be an incentive to improve the documentation on a regular basis.

Hopefully you can see where i'm coming from with this :)