Declared and Undeclared Elements
A declared element is one that is declared in a DTD or schema. If an element is not declared in a DTD or schema, it is an undeclared element. Undeclared elements can appear anywhere inside the root of an XML document because they are not governed by the rules of the DTD or schema. However, when a stylesheet is created from a document type, it will not contain any undeclared elements.
To add undeclared elements from your document, choose > and create the new element with the name you require. You will see a message warning you that the element is not declared in the DTD:
