Music players reading of tags & comments

Support
1

Players playing mp3s with ID3v2.3 tags, I am assuming that they read the
ID3v2.3 internal naming and transpose it to the label, such as
TPE1 = ARTIST and TIT2 = TITLE?

Players playing flac files would read the label definition such as
Artist = Rolling Stones with out any reference any internal naming like TPE1 = ARTIST?
But will they be unable to read any non standard labels like
Label = Mudpie, value and field = %contentgroup%.
Would they be able to read it as CONTENTGROUP and its value?
or it not at all and if so would the song fail to play?

2

depends on player. Generally the answer to above is yes for me (using foobar2000 and LMS for Squeezebox players)

3

Thanks