title: doxygen: custom latex commands not working in html with mathjax
body: <p>I'm writing a documentation.
  I defined a set of custom commands that i give to the doxyfile, using</p>
  
  <pre><code>EXTRA_PACKAGES = ../../user_manual/latex_sources_for_advanced_stuff/extra_basic_commands
  </code></pre>
  
  <p>When I compile the doc to obtain a pdf, it works well. However, in html, it works only if I don't use mathjax, otherwise I get an error:</p>
  
  <pre><code>Undefined control sequence \foobar
  </code></pre>
  
  <p>I don't understand how to also give my package to mathjax ? (if it is possible)</p>
  
  <p>Thanks</p>