DTD definition error

It will get a error to define a dtd as follow:

<!ELEMENT line (property*)>
<!ATTLIST line showType (1|?|+|*) "1" >

The error:

The na开发者_StackOverflowme token is required in the enumerated type list for the "showType" attribute declaration.

It seems the value can't be special characters,such as "?","+","*". To change the characters to Latin-1 characters, like "& #42;"(add a blank before '#') , get the same error.

How to resolve this problem?

Thanks!

It is not possible, as all the enumerated values you specify must be conformant Nmtokens as specified by the XML Recommendation. See http://www.w3.org/TR/xml/#d0e3200.

The BNF for Nmtokens can be seen at http://www.w3.org/TR/xml/#d0e804.