• Colons (:) and underscores (_ ) cannot be used as markup name start characters (UCNMSTRT , LCNMSTRT, or NAMESTRT in the SGML Declaration), though they can be used as non-initial name characters. Although you can use colons and underscores as markup name start characters if you change the system SGML Declaration used for XML document types, we do not recommend this. Since colons are reserved for XML namespaces by the W3C, and Arbortext Editor uses underscores internally for its processing instructions (for example, _font or _link), using them as markup name start characters could cause conflicts.

• Element declarations (the elementdecl production in the XML specification) and attribute declarations (the AttlistDecl production) are not allowed in the internal subset.

• Required markup declarations (the RMDecl production in the XML specification) are ignored and RMD="ALL" is assumed for all XML documents.