[conradludgate]

gzip is not an archive container. You're thinking of .tar.gz which is a "tape archive" format which is compressed using gzip. Zip is by itself both a compression and an archive format, and is what documents like epub or docx use

[gus_massa]

You are right, but other documents like .ggb (GeoGebra files) or .mbz (Moodle backups) use the .tar.gz method. I even wrote programs to opened them, make a few tweaks and save the new version in another compatible file.