I want to create a DTD file but I unfortunately I am getting an error, please advice. Here is my code
<!ELEMENT SUB_CONDITION EMPTY >
<!ATTLIST SUB_CONDITION relation (=|<>|>|<|>=|<=|=Mask|<>Mask) #REQUIRED>
the error is saying: "The name token is required in the enumerated type list for the "relation" attribute declaration."