[php-langspec][PR #234] - Define encoding of PHP scripts (Fix #233)

You can view the Pull Request on github:
https://github.com/php/php-langspec/pull/234

Comment by Agares:
I think the `U+00XX` notation should be avoided, as this notation is usually used to refer to Unicode codepoints. 
If this is an ASCII-compatible encoding of Unicode, then how is `U+0100` encoded? 
And from different side - ISO-8859-2 is ASCII-compatible, but Unicode codepoints are meaningless in context of that encoding.

And sorry that I'm nitpicking on the details, but I believe that as a specification, this document should be as precise as it can be.