Hello, there is an asymmetry between the html-export of latex-formulas by means of dvipng on the one hand and by means of mathjax on the other hand. The asymmetry concerns the handling of information provided by the #+LaTeX_HEADER: parameter. The parameter is taken into account when exporting by means of dvipng, but not when exporting by means of mathjax.
Let me give a small example: *Scenario 1* Say we have a file "test.org" which looks as follows: #+OPTIONS: LaTeX:dvipng #+LaTeX_HEADER: \newcommand{\vd}{\vdash} * Header 1 $\vd$ Now exporting this file into html produces a png image with the "|-" symbol. *Scenario 2* Now our file "test.org" looks as follows: #+OPTIONS: LaTeX:t #+LaTeX_HEADER: \newcommand{\vd}{\vdash} * Header 1 $\vd$ [the only change is in line 1] Exporting this file produces a html file with \vd in red (meaning mathjax doesn't have a subroutine dealing with the command "\vd"). I am not sure if this is the intended behavior. I personally would prefer if the mathjax export would take into account the commands specified in the LaTeX_HEADER. A similar scenario we get with respect to the org-export-latex-default-packages-alist. I have a small style package with all my custom definitions that is listed in org-export-latex-default-packages-alist (with snippet toggled to 't'). Again the LaTeX:dvipng option takes into account the package while the mathjax export ignores it. For the example illustrated in the two examples I used a minimal setup with the following .emacs file: (setq load-path (cons "~/.emacs.d/org-mode/lisp" load-path)) (setq load-path (cons "~/.emacs.d/org-mode/contrib/lisp" load-path)) (require 'org-install) The org-mode is an up-to-date clone from git: M-x org-version returns: Org-mode version 7.7 (release_7.7.264.gbe69) Thanks! Best, Christian