Should a suffix tag always have a value?

[gibson042]

The current grammar prohibits strings like "2021-03-06T16:05:42Z[x-foo]", in which a suffix tag has no value. Should they be allowed?

namespace      = 1*alphanum
namespace-key  = 1*alphanum
suffix-key     = namespace ["-" namespace-key]

suffix-value   = 1*alphanum
suffix-values  = suffix-value *("-" suffix-value)
suffix-tag     = "[" suffix-key "=" suffix-values "]"
suffix         = [timezone] *suffix-tag

[gibson042]

And in a similar vein, should syntax be reserved for accommodating suffix tags whose key and/or value are not limited to alphanumeric ASCII characters? For example, any implementation written against the current text will forever reject strings like "2021-03-06T16:05:42Z[private-example-astral\x20content=\U0001D306]", even though a future version may desire such flexibility.

It might be prudent to structure a grammar in such a way that parsing remains possible and unambiguous, even though there are no currently-defined semantics beyond a requirement to ignore all suffix tags containing unknown content—but on the other hand, that might also be deemed unnecessary complexity. Either way, though, it's worth documenting the rationale for why such a possibility is either intentionally reserved or intentionally precluded.

[ryzokuken]

We considered both and decided it was not necessary to include them. I will try to write a longer explanation soon.