[NTG-context] Choosing an encoding - what are the consequences?

Hi all! I am on the burdensome path to understanding font handling in ConText. Now I wonder what the consequences are with choosing certain encodings. For example if I choose "8a" encoding (called "Adobe standard encoding"): 1. There are lots of empty slots in this encoding. What does ConText do if a symbol that is to be typeset is not contained in an encoding? 2. Can I ommit the 8a encoding in map files when PDF documents are generated (because it is the Adobe standard encoding)? 3. Somewhere I read that "texnansi" is a preferred encoding. Why? Thanks for your attention, --Stefan