Q:

How do I vertically fill a container with uppercase text using JS/CSS? 

I have a text that is uppercase, e.g. ABC. 
As it is uppercase, all characters have the same height. 
I also have a container (div) with fixed height, e.g. 100px. 
How do I make this text fill it vertically, so each letter is exactly 100 pixels high? 
I tried font-size: 100px, but it does not fill the container (there are gaps above and below). 
See http://jsfiddle.net/6z8un/1/ for an example. 
UPDATE 1:
Let's assume all characters actually have the same height (difference either does not exist or is negligible).  Otherwise the question does not make much sense. 
UPDATE 2:
I am pretty sure it can be solved using https://stackoverflow.com/a/9847841/39068, but so far I had no perfect solution with it.  I think ascent and descent are not enough, I would need something else for the top space. 

A:

So far I made a small script that measures letter heights using canvas (would be a good thing to put on GitHub I suppose). 
It is currently slightly unprecise, mostly because of caching. 
I have published it as a library on GitHub, see here: https://github.com/ashmind/textmetrics. 
Unfortunately I did not have time to make demo work as a GitHub page yet, so I can't link to it.