There's some writing in ProgrammingRuby-0.3a in "Standard Types" about % 
quoting. I tried different qouting chars in ruby 1.6.6 and those of 
[0-9a-zA-Z] I tried didnt work.
Its not explicitly stated there you should use punctuation for quoting. 
Perhaps a clarification in the book would solve this? Or have I missed 
something?

BTW: it would be more consistent if strings were quoted %q>string< and 
%q<string> instead of %q>string> and %q<string> but there's no reason 
changing an already working implementation