Tagging standards for Disc and Track

In regards to the TRACK and DISCNUMBER tags, are there any de facto or official standards regarding the total number of tracks/discs as well?

i.e., should TRACK (or DISCNUMBER) be xx/yy or is better to have them stored separately as TRACK xx and TOTALTRACKS xx/yy?

Does it matter between FLAC or mp3 (ID3v2.3)?