Clarify interaction of custom end delimiter versus tag name

[Abscissa]

Suppose a template sets custom delimiters to something that is allowed inside a tag name. The spec isn't clear about what happens.

For example:

• If the end delimiter is set to X and a template contains {{ fooXbar X.... Is the tag's name foo or fooXbar?
• If the end delimiter is set to .X and a template contains {{ foo.Xbar .X.... Is the tag's name foo or foo . Xbar?

Ie: Is the tag defined to be (start delim) (anything *except* end delim) (end delim), or is it more like (start delim) (*anything* that's allowed as part of a tag name) (something that's not allowed as part of a tag name such as }} or trailing-whitespace-followed-by-end-delim), etc) with an error raised if the "something that's not allowed as part of a tag name" doesn't qualify as an expected end tag?

[Abscissa]

Nevermind, it is made clear on interpolation.yml:

The tag's content MUST be a non-whitespace character sequence NOT containing the current closing delimiter.