I guess you weren't there for Be OS, which did let you define your own metadata and then search on them. The bundled mail "application" was what OS X calls a "s

I guess you weren't there for Be OS, which did let you define your own metadata and then search on them. The bundled mail "application" was what OS X calls a "smart folder," a saved search displayed in the filesystem browser. The software that downloaded mail stuck the headers into metadata attributes which the finder-like filesystem browser (the Tracker) could display in sortable columns. Really quite an impressive demo of the technology. The music player worked the same way, relying on other software to copy information out of the ID3 tag into the filesystem metadata so you could search for music by artist, album, year, genre, etc.