XML in a Nutshell, 3rd Edition

Name

External Subset

Synopsis

The document type declaration can include part or all of the document type definition from an external file. This external portion of the DTD is referred to as the external DTD subset and may contain markup declarations, conditional sections, and parameter entity references. It must include a text declaration if the DTD requires features of XML 1.1 or if the character encoding is not UTF-8 or UTF-16:

                        <?xml[ version="
                        version_number
                        "] encoding="
                        encoding-name
                        "?>

This declaration (if present) would then be followed by a series of complete DTD markup statements, including ELEMENT, ATTLIST, ENTITY, and NOTATION declarations, as well as conditional sections, and processing instructions. For example:

<!ELEMENT furniture_item (desc, %extra_tags; user_tags?, parts_list, 
    assembly+)>
     
<!ATTLIST furniture_item
    xmlns CDATA #FIXED "http://namespaces.oreilly.com/furniture/"
>
...