On Aug 19, 2006, at 9:57 AM, Matthew Smillie wrote:

> First, names prefixed with a colon, like :eval, are symbols.  If  
> you're familiar with Lisp, then that's good, because they're quite  
> similar to Lisp symbols.  If you're not familiar with symbols in  
> Lisp, then a quick search of the mailing list archives should  
> provide plenty of explanations for symbols.

This is a very good description of symbols:

http://onestepback.org/index.cgi/Tech/Ruby/ 
SymbolsAreNotImmutableStrings.red

James Edward Gray II