[html-media-capture] The empty string is not defined as conforming value for the capture attribute (#34)

sideshowbarker has just created a new issue for https://github.com/w3c/html-media-capture:

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

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

Please view or discuss this issue at https://github.com/w3c/html-media-capture/issues/34 using your GitHub account