You ask What's the use of "Name" in ... <!DOCTYPE Name SYSTEM "Couple.dtd">
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Like all intentional redundancies, the Name in the XML document type declaration allows for consistency checking. In SGML (from which XML inherited the syntax of the declaration) the checking may be more important, since the document type declaration and the start-tag of the document's outermost element may be in different files or entities. Since XML requires that the document type declaration (if present) be in the same data stream as the tags of the document's outermost element, there is less obvious need for the redundancy in XML, and it would not be too far off to say that the name is retained for compatibility with SGML.