HTML element, attribute, and doctype name validation rules are changing

[domenic]

MDN URL

https://developer.mozilla.org/en-US/docs/Web/API/Element/setAttribute

What specific section or headline is this issue about?

https://developer.mozilla.org/en-US/docs/Web/API/Element/setAttribute#exceptions

What information was incorrect, unhelpful, or incomplete?

In

• Allow more characters when creating various nodes whatwg/dom#1079
• Allow more characters in custom element names whatwg/html#7991
• Remove more XML-derived attribute name validation whatwg/html#11453

we are changing the rules for validating various nodes.

This should affect:

• createAttribute()
• createAttributeNS()
• setAttribute()
• setAttributeNS()
• toggleAttribute()
• createElement()
• createElementNS()
• createDocument()
• createDocumentType()
• customElements: define(), whenDefined()
• dataset's named property setter

I am not sure how many of these are documented on MDN. I found one, for setAttribute(), linked here. It might be good to search for all links to XML Name.

What did you expect to see?

Links to the new definitions in https://dom.spec.whatwg.org/#namespaces .

Do you have any supporting links, references, or citations?

No response

Do you have anything more you want to share?

No response

MDN metadata

Page report details

• Folder: en-us/web/api/element/setattribute
• MDN URL: https://developer.mozilla.org/en-US/docs/Web/API/Element/setAttribute
• GitHub URL: https://github.com/mdn/content/blob/main/files/en-us/web/api/element/setattribute/index.md
• Last commit: bcc977b
• Document last modified: 2025-07-04T17:14:36.000Z

[hamishwillee]

Thanks - we'll look at this when there are implementations. For whoever takes this, the following implementations are linked from whatwg/dom#1079:

• Chrome: https://bugs.chromium.org/p/chromium/issues/detail?id=1334640
• Firefox: https://bugzilla.mozilla.org/show_bug.cgi?id=1773312
• Safari: https://bugs.webkit.org/show_bug.cgi?id=241419