I started making a few edits based on Zuo and Walter's comments while getting this patch ready for merging, and decided the end result could benefit from an additional round of feedback before committing it.

This particular patch is also aimed at the Python 3.4 maintenance branch rather than at trunk - the introduction of the new namereplace error handler in 3.5 means that the previous patch didn't apply cleanly to the maintenance branch.

While Zoinkity's feedback is also valid (i.e. multibyte codecs aren't documented properly, custom codec registration is both harder than it really should be and not well documented), I think those are better filed and handled as separate issues, rather than trying to handle them here as part of the general "bring the current content of the codec module documentation up to date with the current state of Python 3".