When browsing a markdown file in Diffusion with the 'View as Remarkup' view option selected, the file will render in HTML, but no TOC (table of contents) will be generated
Eg: https://we.phorge.it/source/phorge/browse/master/externals/octicons/README.md?as=remarkup
The code for generating the TOC exists (see src/infrastructure/markup/blockrule/PhutilRemarkupHeaderBlockRule.php) but it is not used in Diffusion.