Content Models and Datatypes

Unordered content. Required content without a required order (approximately the SGML "&" connector).

Simple datatypes. Dates, integers, prices, etc.

Enumerations. Enumerated attribute and element content.

Default values. Default attribute and element values.

Pattern matching. Attribute and element content validity based on patterns (e.g., regular expressions).

Exclusions.

Pernicious mixed content. Restrictions on mixed content.

Empty mixed content. Mixed content elements that have no required content but may not be completely empty.