EXTENDED HEADER OVERVIEW (optional)
The extended header contains information that can provide further insight in the structure of the tag, but is not vital to the correct parsing of the tag information; hence the extended header is optional.
Extended header size 4 * %0xxxxxxx Number of flag bytes $01 Extended Flags $xx
Where the 'Extended header size' is the size of the whole extended header, stored as a 32 bit synchsafe integer. An extended header can thus never have a size of fewer than six bytes.