During the development of scripts for the Discogs WS I found the following two points regarding the documentation and implementation of the id3-standard in mp3tag.
- Mp3tag claimes in its documentation https://docs.mp3tag.de/mapping/, that there exists a tag field named "GROUPING" in id3v2.3 and id3v2.4 with header GRP1. This frame can't be found in the id3-documents under https://id3.org/Developer%20Information. Perhaps this tag field only exists for matroska file format? In this case the mp3tag-documents should be corrected.
- Similar to the "Copyright Message" TCOP frame the id3-documents define for id3v2.4 a "Produced Notice" TPRO frame, in which the string must begin with a year and a space character, followed by the production copyright holder of the original sound. Every time this field is displayed the field must be preceded with "Produced " (P) " ", where (P) is one character showing a P in a circle.This feature seems to be missing in mp3tag and I would like it to be added, so that I am able to make experiments with it.