I\'m using the fragment identifier to create a permalink for AJAX events in my web app similar to this guy. Something like:
http://www.myapp.com/calendar#fi
See the RFC 3986.
fragment = *( pchar / "/" / "?" )
pchar = unreserved / pct-encoded / sub-delims / ":" / "@"
unreserved = ALPHA / DIGIT / "-" / "." / "_" / "~"
pct-encoded = "%" HEXDIG HEXDIG
sub-delims = "!" / "$" / "&" / "'" / "(" / ")"
/ "*" / "+" / "," / ";" / "="
So you can use !, $, &, ', (, ), *, +, ,, ;, =, something matching %[0-9a-fA-F]{2}, something matching [a-zA-Z0-9], -, ., _, ~, :, @, /, and ?