The macros in vulkan-macros.rb and vulkan-macros/extension.rb are described in the “Vulkan Documentation and Extensions: Procedures and Conventions” document (see the styleguide).
Asciidoctor is customized to insert KaTeX <script> tags from math.js for HTML5, and properly pass through math which has \begin{}\/end{} delimiters instead of $$[]().
For PDF builds, asciidoctor-mathematical is used to generate
math-docbook.conf is heavily conditionalized depending on whether the final output format (which should be described in the a2x-format variable) is pdf or not, since Docbook passes through math differently to dblatex vs. the XHTML stylesheets. This could be simplified now that we're only using Docbook for PDFs.
khronos.css is the stylesheet used for HTML output.