whitespaces, need a help !

["Vladimir V. Popov" <vladimir.popov@arcadia.it>]

                                                10:52 AM                                                
                                                Tuesday, May 22, 2001
                                                ARCADIA S.p.A.    
                                                35 G.Fara St.
                                                20124 MILAN, Italy

Dear All,

  I have a xml data with elements which contain only whitespace(s).
  These elements are very important because this xml is banking
  exchange information and sometimes these elements may contain
  information. I have to produce *.xsd to validate this *.xml.
  Does anybody know how can I check and constrain these elements for
  using, for example, only such chars (UTF-16): #x0020, "I", "E"?

Yours sincerely,
  Dr. Vladimir V. Popov           reply to: vladimir.popov@arcadia.it