[nsp] IOS Naming convention

[Jason Lixfeld]

Not sure if this is a broken record topic or not, but I'm curious as to 
wether there is  a document which specifically identifies the different 
IOS trains and what trains are for what, exactly.  For example,  I was 
running 12.2(15)T5 on a VXR and I want to use IPSec Stateful Failover 
for High Availability VPN.  That feature is supported in 12.2(11)YX, 
not 12.2(15)T5.  Is there a document that says YX is for blah, T is for 
Technology, B is for Broadband, ZY is for blah, etc?