Some initial thoughts on structuring error  & warning messages.

Proposed regexp:
  /^(Error|Warning|Fatal)(:\S*)*\s+(.*)$/

Eg.
  Error:undefined:\somemacro The macro \somemacro is undefined.
or
  Warning:mathparse:somerule Unrecognized pattern blah blah.


Try grepping for Error and Warning to generate a set of
useful keywords:

Error:unexpected:?  A <box> was supposed to be here
Error:unexpected:\else  Stray \else ...
Error:unexpected:?  Non-relation token
Error:unexpected:\endcsname

Error:unexpected:&

Error:missing_file:$path

Error:redefinition:\foo

Error:undefined:\foo

Error:cant_create:$file Couldn't create file

Warning:unexpected: