Do POSIX classes work in regular expression searches?

["Mark S" <throaway@yahoo.com>]

I've been trying to do some simple searches like:

  (query-replace-regexp "<span[:ascii:]*?</span>+" "test")


or even the simpler

  (query-replace-regexp "[:ascii:]*" "test")

and not getting anywhere. Emacs just looks for the characters ":acis" --  
not for the POSIX character set of all ASCII characters. Trying it with  
other sets also got me nowhere. These character classes are listed in the  
Emacs documentation -- is there a trick to getting them to work?

Thanks,
Mark

GNU Emacs 23.2.1 (i386-mingw-nt5.1.2600)
  of 2010-05-08 on G41R2F1