Should the Host Language Label be used if it's empty?

[dandclark]

The Host Language Label step E of the accname computation algorithm is unclear on whether the empty string should be used if that's what the native markup provides.

E. Host Language Label: Otherwise, if the current node's native markup provides an attribute (e.g. alt) or element (e.g. HTML label or SVG title) that defines a text alternative, return that alternative in the form of a flat string as defined by the host language, unless the element is marked as presentational (role="presentation" or role="none").

Going by a strict reading of the spec, I'd guess that an empty string should be used. However the img with tooltip label with empty alt subtest of accname/name/comp_tooltip.html suggests that an empty alt attribute should be ignored. Gecko and WebKit pass this test, while Blink fails.

If that test reflects the intended behavior, should the spec be updated to something like this?

E. Host Language Label: Otherwise, if the current node's native markup provides an attribute (e.g. alt) or element (e.g. HTML label or SVG title) that defines a text alternative, return that alternative in the form of a flat string as defined by the host language, unless the text alternative is an empty string or the element is marked as presentational (role="presentation" or role="none").

Also -- if the empty string is omitted, what about a whitespace-only string? (See #233).

[scottaohara]

related w3c/html-aam#533

[aleventhal]

Not that it answers this question, but I wanted to note that <img alt=""> is special. It historically was a way to indicate decorative/redundant images before ARIA existed. The presence of an alt attribute with the empty string tells screen readers like JAWS to not attempt to repair the missing alt attribute. We can't really break that since it's baked into the web at this point. But whether aria-label[ledby] should override that is another question.

[MelSumner]

The test reflects the desired behavior but alt="" is special TBH.

I have long been of the opinion that, since modern IDEs will pre-fill <img src="" alt=""/> for you, it should be permissible/valid to also add role="none" or role="presentation" to an image.

I do not think the specification should change here. If anything, we could add a note that this is a special case.

[MelSumner]

TL;DR:

• Question: Should the host language label be used if it's empty?
• Answer: Yes.

Here's the long answer.

If I'm understanding the question correctly, I think the question boils down to this:

if the native markup provides an empty string as a text alternative (e.g., an empty alt="" on <img>), should that empty string be used as the accessible name?

Correct Interpretation: An Empty String Should Be Used

A strict reading of the spec suggests that "if the host language provides an empty string, it must be used as the accessible name".

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Evidence Supporting This Interpretation

1. The Spec Says "Return That Alternative"

   • Step E states:

     "return that alternative in the form of a flat string as defined by the host language."

   • If the host language (e.g., HTML) defines that an empty string ("") is a valid alternative text, then returning "" is the correct behavior.

2. HTML and ARIA Best Practices Align with This

   • In HTML, alt="" explicitly conveys that an image should be ignored by screen readers.
   • The same logic applies to <title> elements inside SVGs:

     <svg>
       <title></title> <!-- Empty title -->
       <rect width="100" height="100" />
     </svg>
     Since the title exists but is empty, its contribution to the accessible name would be "", resulting in no name for the SVG.

3. Precedent from ARIA aria-labelledby=""

   • If aria-labelledby references an element that exists but is empty, the computed accessible name is an empty string, not null.

     <label id="label"></label>
     <input aria-labelledby="label">
     • Accessible name: "" (empty string).
     • The element is not unnamed (null), but explicitly has an empty string as its name.

4. Consistent Behavior with Host Language

   • HTML <img alt=""> → Exposed as name="" (not null).
   • SVG <title></title> → Exposed as name="" (not null).
   • ARIA aria-labelledby="" → Exposed as name="" (not null).

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Why This Matters

• Empty strings signal intentional omission. This is particularly important for images (alt="" means "decorative, ignore me").
• Returning null vs. "" changes behavior. If the accessible name computation returned null, an element might fall back to other naming mechanisms (e.g., child text content), which would be incorrect.
• Preserves fidelity with native behaviors. The computed name should reflect what is actually present in the DOM, even if it is an empty string.

---

Conclusion

✅ The correct interpretation of Step E is that an empty string ("") must be used if the host language provides it.
🚫 The accessible name should not be null or undefined unless no alternative text mechanism is provided at all.