I want to place some customization codes in a separate file, and include it
from other files later. For example, file config.org has a single line
#+MATHJAX:
align:"left" mathml:t. How do I include it in another .org file abc.org so
that the net-effect is exactly same as I write that #+MATHJAX line directly
in abc.org (#+INCLUDE doesn't meet this requirement)? Thanks.

-- 
Regards,
Zihan, Sheldon Liu
------------------------
The Media Computing Group (MCG)
where Media Spectrum unleashes Digital Potential for Fun in Life.

School of Creative Media (SCM)
City University of Hong Kong