The empty string is not defined as a conforming value for the capture attribute

[sideshowbarker]

At https://w3c.github.io/html-media-capture/#the-capture-attribute the spec states:

The attribute's keywords are user and environment, which map to the respective states user and environment.

…but the spec does not define the empty string as a conforming keyword.

Because the spec doesn’t define the empty string as a conforming keyword, the following example from the spec itself doesn’t conform to the actual requirements in the spec —

<form action="server.cgi" method="post" enctype="multipart/form-data">
  <input type="file" name="audio" accept="audio/*" capture>
  <input type="submit" value="Upload">
</form>

[anssiko]

If the attribute value matches none of the given keywords, the invalid value default maps to an implementation-specific state that indicates to the implementation to act according to its default behavior. IIRC this design was for historical reasons.

[sideshowbarker]

If the attribute value matches none of the given keywords, the invalid value default maps to an implementation-specific state that indicates to the implementation to act according to its default behavior.

That applies to the action of the implementation, which is orthogonal to the document-conformance requirements (authoring-conformance requirements). The issue is that the document-conformance requirements explicitly state that user and environment are valid keywords, but don’t explicitly state that the empty string is a valid keyword.

For the empty string to be considered a valid value that documents and authors are allowed to use, it must be explicitly included in the same spec sentence that begins with The attribute's keywords are user and environment.

Compare to https://html.spec.whatwg.org/multipage/interaction.html#contenteditable:

The contenteditable content attribute is an enumerated attribute whose keywords are the empty string, true, and false.

Or compare to https://html.spec.whatwg.org/multipage/media.html#attr-media-preload, which states that for thepreload attribute, The following table lists the keywords and states for the attribute, and then lists none, metadata, and auto, followed by this statement:

The empty string is also a valid keyword, and maps to the Automatic state.

[anssiko]

@sideshowbarker thanks for the clarification, PTAL #35