Highlights.jl has received some recent updates that switch out the internals to use treesitter (via TreeSitter.jl) language grammars instead of the home-brew system I implemented originally. This has been a long time in the making: Julia Syntax highlighting on websites - #17 by mike.
Please note that this is a breaking change, though hopefully most users will be able to migrate to 0.6 relatively easily (if not then feel free to ping me for assistance), and also find the improved grammars and resulting highlighting quality worth the effort to migrate.
All the previously built-in languages that were available are now available as self-contained JLLs that provide the treesitter-based grammars (plus highlighting queries for those grammars), for example tree_sitter_julia_jll. Plus there’s many other grammars already available as JLLs, and it’s very straightforward to wrap ones that aren’t available yet.
Aside from the grammars being overhauled, the theme system has be updated as well to make use of external theme data from the Gogh project. This provides a wide range of popular themes. Support for custom themes is still available.
See the docs for more details on the new API. Happy highlighting!