References

Martin Nilsson, ID3 tag version 2.3.0.

Martin Nilsson, ID3 tag version 2.4.0 - Main Structure.

M. Nilsson, "ID3 tag version 2.4.0 - Native frames.

S. Bradner, "Key words for use in RFCs to Indicate Requirement Levels", RFC 2119, March 1997.