begin maruku_doc

 Extension: math
 Attribute: html_math_engine
 Scope: document, element
 Output: html
 Summary: Select the rendering engine for MathML.
 Default: <?mrk Globals[:html_math_engine].to_s ?>

 Select the rendering engine for math.

 If you want to use your custom engine `foo`, then set:

   HTML math engine: foo
 {:lang=markdown}

 and then implement two functions:

   def convert_to_mathml_foo(kind, tex)
     ...
   end

end