The current postprocessing framework works by passing the document through a sequence of postprocessing filter modules. Each module is responsible for carrying out a specific transformation, augmentation or conversion on the document. In principle, this architecture has the flexibility to employ new filters to perform new or customized conversions. However, the driver, latexmlpost, currently provides no convenient means to instanciate and incorporate outside filters, short of developing your own specialized version.
Consequently, we will consider custom postprocessing filters outside the scope of this manual (but of course, you are welcome to explore the code, or contact us with suggestions).
The two areas where customization is most practical is in altering the XSLT transforms used and extending the CSS stylesheets.