DTD definition error

Question

Hi,

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

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

The error:

The name 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!