Maintenance status

[romainmenke]

Hi @lahmatiy,

I am one of the maintainers of Stylelint.

In Stylelint we use csstree to validate the values for each property.
The rule in question isn't part of a standard config but we are hoping it might be in the future.
We think that this kind of validation is really valuable for CSS authors.

This rule is very similar to https://github.com/csstree/stylelint-validator

---

Since creating this rule we have encountered various false positives/negatives because the syntax data published with csstree is starting to fall behind.

We are unsure what the current status is of csstree and if regular updates might resume in the future?

Having a bit more insights into the status of csstree would help us pick a path forwards.

An equally valid path forwards would be for us to maintain our own dataset but we rather contribute here so that more people can benefit from these updates.

Thank you in advance

[romainmenke]

@lahmatiy Just want to already give a massive thank you for the recent fixes and the release of v3.0.0. We really appreciate the effort you put into csstree 🙇

[lahmatiy]

@romainmenke Thank you for your support and kind words.

Regarding the maintenance status. There are some longstanding issues in CSSTree and non-ideal solutions that need attention. I’d like to address these, but I currently lack the resources. My focus is on a different projects (CPUpro), which keeps me quite busy. However, I hope to find some time to implement new features and resolve issues, though I can't predict when that will happen.

As for the false positives/negatives, many (though not all) stem from the dictionary. CSSTree relies on mdn/data with some custom patches. However, since mdn/data is sunsetting in favor of webref, this presents a challenge. While webref is valuable, it reflects the state of specs rather than real-world. The key challenge here is creating a robust CSS syntax dictionary, ideally combining webref, manual automated approvals, and patches for legacy and non-standard elements, tailored for projects like CSSTree (e.g., for linting, validation, syntax matching, etc.). While can't drive such an effort, it's clear that CSSTree would greatly benefit from it.

I also experimented with testing CSSTree validation on real-world CSS (see real-web-css). I believe that projects like this can significantly enhance the quality of validation by providing insights into how CSS is used in the wild, beyond what's specified in formal standards. Such testing helps identify edge cases and non-standard patterns, allowing for more accurate validation and better support for real-world scenarios. It also aids in refining the syntax dictionary and improving the overall robustness of CSSTree.

In addition to that, future priority work includes:

• Relaxed CSS nesting
• More flexible parsing of values/selectors/at-rules (e.g., generating Token/Raw nodes instead of throwing errors)
• Selector validation
• calc()/math/etc functions, which can be used anywhere regardless of property syntax
• Per-function validation (including preventing media/supports/container queries from falling into general enclosures, which can cause false positives)
• General rules validation (e.g., unknown units/functions/keywords, dashed identifiers for var(), etc)
• Syntax definition updates (e.g., Functional Notation Definitions #292, semicolon as a dividers, etc)

[romainmenke]

Thank you for this update @lahmatiy 🙇

It is nice to hear that there are still plans for CSSTree :)
It is a really awesome project.

---

I agree that the mdn/data and webref situation is complex.
Ideally mdn/data would remain or would be replaced by a similar effort.
Purely scraping the CSS specs is not sufficient.

I've been working on a series of patches for the CSSTree dictionary : https://github.com/csstools/postcss-plugins/blob/main/packages/css-syntax-patches-for-csstree/README.md#css-syntax-patches-for-csstree End users that want to write bleeding edge CSS can use this package. Hopefully this removes some of the pressure to always be up to date here in CSSTree.

---

If there is anything that would aid you directly, please let me know.

Otherwise this can be closed as answered :)

[nzakas]

@lahmatiy we are also starting to use CSSTree in ESLint. It's a great project and we'd like to be able to contribute back. I know you're busy on other projects, so I'm wondering if you'd be open to adding some other maintainers to the project? I feel like this is an important project and I think there are those on the ESLint and Stylelint teams that would likely be willing to help out.

[carlosjeurissen]

@lahmatiy Friendly reminder for the PR adding stylelint 16 support to the stylelint-validator:
csstree/stylelint-validator#59 (comment)