DTD - element
Translation results：
Document type definitions (DTDs) define legal building blocks for XML documents. It uses a series of legal elements to define the structure of the document.
A DTD can be declared in an XML document as a line or as an external reference.
DTD - elementsyntax
In a DTD, elements are declared through element declarations.
DTD - elementexample
<!ELEMENT element-name EMPTY> 实例: <!ELEMENT br EMPTY> XML example: <br />