If a document is syntactically correct it can be called as well-formed XML documents. A well-formed document conforms to XML's basic rules of syntax:
Every open tag must be closed.
The open tag must exactly match the closing tag: XML is case-sensitive.
All elements must be embedded within a single root element.
Child tags must be closed before parent tags.
A well-formed document has correct XML tag syntax, but the elements might be invalid for the specified document type.