Invalid character found [dtd]

Friends,
I am writing a stylesheet for EAD 2002 XML tag set (into PDF). I am
writing it against the DTD. I wanted to make the DTD more exact. The
problem I have is that the syntax in the ATTLIST has an illegal
character "/". Anyone have any idea how I can change the DTD so that
it will accept the "/" character as an attribute value?

Examples below.

Thanks,
Mike Ferrando
Washington, DC

DTD available at:
http://www.loc.gov/ead/ead2002a.html

SAXON error text:
  Invalid character found in ATTLIST enumeration.
  URL: file:///C:/WORKSHOP/documents/ead_1.dtd
  Line 02970:     (box-folder | box/folder | reel | mapcase | folder
| box)
  Pos  00022: ---------------------^

ead XML
<CONTAINER TYPE="box/folder">3/4</CONTAINER>

ead.dtd (2002)
<!ELEMENT container
   (#PCDATA | %m.phrase.basic;)*
                                                                     
       >
<!ATTLIST container
   %a.common;
   %am.container.label;
   %am.container.type;
   %am.container.encodinganalog;

   parent
    IDREFS
    #IMPLIED

ead_1.dtd (What I want.)
<!ELEMENT container
   (#PCDATA | %m.phrase.basic;)*
                                                                     
       >
<!ATTLIST container
   %a.common;
   %am.container.label;
   %am.container.encodinganalog;

   type
    (box-folder | box/folder | reel | mapcase | folder | box)
    #IMPLIED

   parent
    IDREFS
    #IMPLIED




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