Secure XML: The New Syntax for Signatures and Encryption

3.4. XML Document Logical Structure

The logical structure of an XML document consists of declarations, elements, character references, comments, and processing instructions.

Table 3-4. Structure of an XML Document

Structure	Consists of…	Part Referred to as…	Notes
Logical	Markup	Declarations Elements Attributes Character references CDATA sections Comments Namespaces Processing instructions	Explicit markup indicates each type of markup. The logical and physical structures must nest properly.
Physical	One or more storage units	Entities	Entities have content and a name. They can be parsed or unparsed. They can refer to other entities. Each document has a document entity. All have content. All are identified by name, except the document entity and an external ...