Nice!
Where can I find the meaning of the alpha characters?
Well that varies by airline... generally speaking, the further to the "right" it is, then the cheaper the ticket and the more restricted.
So for a little education, in the example I pulled was for a United Airlines Flight (and I am not a super expert but consulted with an airline for 2 years and learned some of their dirty tricks):
F9 - Means there are at least 9 first class tickets available
Y9 - Means there are at least 9 coach tickets available
B9M9 - Typical "semi-restricted" seats here
E9U9H9Q9V9W9S9T0K9 - Cheap economy fares with lots of restrictions
L0G0P9A9 - Special fares that normal people usually can't get
But basically this class has a bearing on the fare basis for the flight, which is another code they use internally to figure out the actual price for the ticket. You will only see this on your receipt. There is a big block of text on most receipts and you are looking for a code right after the cost of the ticket. For example a recent flight for me was SE14A1N which meant that is was a "S" class ticket 14 advanced purchase with restrictions.
The biggest problem with this is these are the tickets the airline will let you sell, not really how many seats that are truly left. Airlines almost always oversell flights (as you probablly know) and I have often seen it where you will see seats available when the flight is way oversold. The airline has access to the real "load" numbers but they are not allowed to share them, even with travel agents. When I was consulting I used to have access to see if a flight really had seats on it or not, but alas now, I have to call in favours.