
Document Type Definitions (DTD) • 135
Entities are used to define reusable pieces of text. It is declared in DTD as <!ENTITY Entity name
"entity value"> and are referred in the XML as &Entity name;.
An attribute declared as of type NMTOKEN (name token) could contain letters, digits, periods,
underscores, hyphens, and colon characters.
An enumerated attribute allows us to specify the list or set of possible values that the attribute can
have.
The conditional sections are used to include or ignore the part of the DTD declarations. They are
indicated by the use of two keywords: INCLUDE and IGNORE. They are declared as: <![keyword