This is a special token in that it can only occur at the beginning of
documents. If a BOM byte mark occurs elsewhere in a file, it should
be treated as PPI::Token::Whitespace. We recognize the byte order
marks identified at this URL:
UTF-32, big-endian 00 00 FE FF
UTF-32, little-endian FF FE 00 00
UTF-16, big-endian FE FF
UTF-16, little-endian FF FE
UTF-8 EF BB BF
Note that as of this writing, PPI only has support for UTF-8
(namely, in POD and strings) and no support for UTF-16 or UTF-32. We
support the BOMs of the latter two for completeness only.
The BOM is considered non-significant, like white space.