1. Package parameter `xhtml'

This parameter asks for a XML version of the HTML 4.0 output.

2. \Hinclude[*]{mathml.4ht}

These commands ask to load the named files. The commands should appear before the \Preamble instruction.

3. Package parameters `mathml.4ht' and `unicode.4ht'

4. -i/.../ht-fonts/unicode/
unicode/! as second parameter of htlatex

This switch of the tex4ht utility asks for unicode fonts in the output.