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Top-level
 As a first step you need to define the various highlight styles in your CSS using `::highlight(x)` and also register them in the registry using `CSS.highlights.set(x, new Highlight())` (x being the types of tokens: comment, property, boolean, class-name, etc.) 30 comments
The Custom Highlight API is supported in Chrome 105+ and Safari 17.2+. Firefox has experimental support.   @bramus @hi_mayank The Pen worked for me in Firefox Nightly, so it appears MDN is accurate on this. Also, I don’t understand how it works, because your script and style blocks don’t have all the `span`s around highlighted stuff, but the Prism home page’s code blocks do have all those `span`s. So how Prism helps here is completely opaque. @hi_mayank @Meyerweb I have prism set up in manual mode, meaning it doesn't automatically kick in. I then manually call it to tokenize the code. This gives me a bunch of numbers about which token is where and what type it is. This info is then used to populate the Custom Highlight API. @bramus @hi_mayank @Meyerweb I think a next step towards a declarative API—one that doesn’t require JS—would be some way of teaching the browser grammars using something like PEG. Then you could set an attribute on a `<code>` element to specify which grammar you want to be used for it to auto-tokenize and highlight that code block. @knowler @hi_mayank @Meyerweb I don’t think that would work. Which languages do you include? Which versions of those languages? When do these definition files get updated? Would you be able to load your own? … Reminds me of authors requesting to put jQuery in the browser. Same questions arose. (We actually got that last thing … not by including jQuery in browsers but by having better JavaScript/DOM APIs nowadays) @develwithoutacause @bramus @hi_mayank @Meyerweb Ya, that sort of API is kinda what got me thinking about using grammars. I do think that would still be a really nice low cost API though. Scales down alright, even though you’d probably need a tool to manage it (otherwise… lots of counting and attention to whitespace). @knowler @bramus @hi_mayank @Meyerweb Yeah, definitely would need to be generated by a tool. @bramus @hi_mayank I think I grasp what you’re saying, but is there an article or something that breaks this sort of thing down in detail? @Meyerweb @hi_mayank Sorry, not yet. My typical flow is hack it together, put it on socials, and then maybe later write about it. What could help you better understand is to console.log(tokens) right after Prism has done its thing. MDN might also have some good info (I'm afk right now, so can't check)  @bramus @Meyerweb @hi_mayank I'm curious too, need to do some sleuthing. This clearly wants to be a custom element, right? No shadow dom required, and the progressive enhancement story is "just add color". A perfect use-case. @mia @bramus @Meyerweb and then you plug the token positions into ranges (and the token types and ranges into highlights): https://developer.mozilla.org/en-US/docs/Web/API/CSS_Custom_Highlight_API#create_ranges @hi_mayank @mia @bramus @Meyerweb just trying to get my head around it - looks like key JS requirement is creating and registering the text ranges - and to do this requires a start an end "position" - so presumably you could "tokenise" somewhere other than the client as long as you shipped this big list of number pairs and types with each code example? Would maybe assume that with a large number of code examples it is very quickly less bytes to do it all clientside though - just thinking aloud…  @bramus @hi_mayank Seems to be working in Dev Edition with the about:config option turned on. If you want to know the details: did a full write up on this one: https://www.bram.us/2024/02/18/custom-highlight-api-for-syntax-highlighting/ Also comes with an extra demo that syntax highlights the code in a [contenteditable] as you type. @bramus It’s interesting that this new approach prevents you from using many CSS features. I’m using Highlight.js to syntax-highlight code for LaTeX (to produce PDFs from Markdown). And I had to look up sequences of CSS class names in CSS files to get color, text weight, etc. That’s what you need to do here, too. It’s a shame there is no declarative (non-JS) version of this API. |
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With that in place, and after tokenizing code snippets (e.g. using @prismjs), it’s only a matter of assigning the tokens to the corresponding Highlight.
`CSS.highlights.get(token.type).add(range)`