I understand the basic concept that DTDs used for XML validation. However, it seemds kinda odd that it's the xml document that will refer to the DTD thru the DOCTYPE element. Let's say the sender and the receiver agree upon a specific format for the xml document they exchange, and the receiver can validate the xml document, using an agreed upon DTD. Now, if the sender sends an xml document that does NOT include a DOCTYPE element, the receiver can no longer validate the document, and whole purpose of defining the DTDs is defeated. Doesn't it make more sense to send the DTD as a parameter to the validating parser, and have the parser validate the xml document? Am I missing some thing?