The difference between LaTeX's input and output encodings has been discussed in various places; I especially like user @egreg's answer here.
There is however an aspect of dealing with output encodings that I do not understand: When a user loads multiple output encodings, how does LaTeX decide and know which one to use at any given time during compilation?
For example, the documentation of tipa
has an example where the user loads three output encodings:
\documentclass{article}
\usepackage[T3,OT2,T1]{fontenc}
\usepackage[noenc]{tipa}
Also, why don't packages or languages that require certain output encodings load these themselves? That is, why does the user have to decide which ones to load via fontenc
's options?