[php-langspec][Issue #233] - Unicode codepoints are used in the specification, but the specification does not define encoding

You can view the Issue on github:
https://github.com/php/php-langspec/issues/233

Opened By: Agares
Issue Description:
For example here:
https://github.com/php/php-langspec/blob/master/spec/19-grammar.md#grammar-name-nondigit
"one of the characters U+0080–U+00ff"

This statement is ambiguous if the encoding is not defined. What I believe would be correct is saying that PHP uses ASCII, but byes 0x80 to 0xFF might be allowed, as defined in the grammar, and then the grammar should read "one of the bytes 0x80 – 0xFF"