Object of the type PPI::Token::Unknown exist primarily inside the
tokenizer, where they are temporarily brought into existing for a very
short time to represent a token that could be one of a number of types.
Generally, they only exist for a character or two, after which they are
resolved and converted into the correct type. For an object of this type
to survive the parsing process is considered a major bug.
Please report any PPI::Token::Unknown you encounter in a PPI::Document
object as a bug.