HTML enumerated attributes are case-insensitive

[Elchi3]

Description

In HTML everything is case-insensitive including enumerated attributes and their values.

Motivation

Estelle motivates me.

Additional details

See step 2. in https://html.spec.whatwg.org/multipage/common-microsyntaxes.html#enumerated-attribute

Related issues and pull requests

#40260 (comment)

[github-actions]

Preview URLs

• /en-US/docs/Glossary/Enumerated
• /en-US/docs/Web/API/Document_Object_Model/Reflected_attributes

Flaws (2)

Note! 1 document with no flaws that don't need to be listed. 🎉

URL: /en-US/docs/Web/API/Document_Object_Model/Reflected_attributes
Title: Attribute reflection
Flaw count: 2

• macros:
  • Macro produces link /en-US/docs/Web/API/Document_Object_Model/Events which is a redirect
  • Macro produces link /en-US/docs/Web/API/Document_Object_Model/Whitespace_in_the_DOM which is a redirect

External URLs (2)

URL: /en-US/docs/Glossary/Enumerated
Title: Enumerated

• https://html.spec.whatwg.org/multipage/common-microsyntaxes.html (2 times) (Note! This may be a new URL 👀)

---

URL: /en-US/docs/Web/API/Document_Object_Model/Reflected_attributes
Title: Attribute reflection

• https://html.spec.whatwg.org/multipage/common-microsyntaxes.html (1 time) (Note! This may be a new URL 👀)

(comment last updated: 2025-07-17 08:22:31)

[Josh-Cena]

Shall we mention that their IDL-reflected properties always return the lowercase variant, given that was what the original comment was interested in?

[Elchi3]

Shall we mention that their IDL-reflected properties always return the lowercase variant, given that was what the original comment was interested in?

Added but talked about "canonical values per specification" as I didn't find spec text that says that enumerated values will always return lowercased via IDL reflection. Did you see that?

[Josh-Cena]

I think that's just by convention. You are right that technically it can be specified to be something else

[hamishwillee]

Nice, nit proposal for you in https://github.com/mdn/content/pull/40377/files/44a41ea34232a02bb6cc8b95a45f095f312fff5f..53e3f6addc3feff788dc3f33062e7f566fd0f890#r2211660420 but otherwise good.