etc-gentoo/texmf/texmf.d/00header.cnf

% original texmf.cnf -- runtime path configuration file for kpathsea.
% Public domain.
% 
% If you modify this original file, YOUR CHANGES WILL BE LOST when it is
% updated.  Instead, put your changes -- and only your changes, not an
% entire copy! -- in ../../texmf.cnf.  That is, if this file is
% installed in /some/path/to/texlive/2015/texmf-dist/web2c/texmf.cnf,
% add your custom settings to /some/path/to/texlive/2015/texmf.cnf.
% 
% What follows is a super-summary of what this .cnf file can
% contain. Please read the Kpathsea manual for more information.
%
% Any identifier (sticking to A-Za-z_ for names is safest) can be assigned.
% The `=' (and surrounding spaces) is optional.
% $foo (or ${foo}) in a value expands to the envvar or cnf value of foo.
% Long lines can be continued with a \.
%
% Earlier entries (in the same or another file) override later ones, and
% an environment variable foo overrides any texmf.cnf definition of foo.
%
% All definitions are read before anything is expanded, so you can use
% variables before they are defined.
%
% If a variable assignment is qualified with `.PROGRAM', it is ignored
% unless the current executable (last filename component of argv[0]) is
% named PROGRAM.  This foo.PROGRAM construct is not recognized on the
% right-hand side. For environment variables, use FOO_PROGRAM.
%
% Which file formats use which paths for searches is described in the
% various programs' and the Kpathsea documentation (http://tug.org/kpathsea).
%
% // means to search subdirectories (recursively).
% A leading !! means to look only in the ls-R db, never on the disk.
% In this file, either ; or : can be used to separate path components.
% A leading/trailing/doubled path separator in the paths will be
%   expanded into the compile-time default. Probably not what you want.
%
% Brace notation is supported, for example: /usr/local/{mytex,othertex}
% expands to /usr/local/mytex:/usr/local/othertex.  We make extensive
% use of this.