Invalid XML declarations allowed

[wt]

The parser allows XML declarations anywhere in the file. If a declaration exists it should be at the very beginning of the file.

Also, only one declaration should be allowed.

Both of these constraints are not currently enforced.

More info on the validity of xml declarations is here.

[Mingun]

I think, this is by desing, but we can have a setting to enforce checks, and definitely should have this checks for serde deserializer

[wt]

It would also be useful to have a Reader/NSReader capable of enforcing such a thing for when I know there is only one document in a file/str source.

[Mingun]

Yeah, I say exactly this -- add a setting to enforce this behavior