ID3 specifications
I downloaded these from the net. For v1 specs see appendix in back of 2.0 spec
id3 version 2.0
id3v2.00 spec commented
id3v2-00.txt
id3 version 2.3
id3v2.3.0 spec text
id3 version 2.4
id3v2.4.0-structure.txt
id3v2.4.0-frames.txt
id3v2.4.0-changes.txt