Developer's Guide to Web Application Security

order. Schemas also provide a means for specifying element and group quantities,

defining attributes, set default attribute values, defining data types, and data type

constraints for both elements and attributes. Schemas allow for very granular control

of the structure of elements.

Schemas also allow for providing an open or a closed content model. An open

content model allows for the extension of structures by others by allowing the addi-

tion of elements to the document. A closed content model restricts the flexibility of

the content but is much more stable. Whether you define your schema using a closed

or open content model depends on how you plan to ...