I tried to follow the links above to the Official abc Notation Site but the University of Greenwich website doesn't recognise that address anymore. Is there a new location for comprehensive ABC information? I would like to learn more about advanced features like synchronised lyrics, since ABC is a portable format I can actually read or write without extra hardware or software.
I haven't figured out what the backslash \ means in ABC files (found through JC's ABC Tune Finder through DigiTrad Power Search) such as Erich Rickheit's conversion of The Streets of London. (This clicky doesn't work: http://sniff.numachi.com/~rickheit/dtrad/abc/STLONDON.abc.)