Essential XML: Beyond Markup

Content Models and Particles

Complex type definitions specify the constraints on the [children] and [attributes] for a given type of element information item. The content model of an element's [children] is composed of particles. A particle is a local element declaration or reference to a global element declaration (element), a compositor (sequence, choice, or all), a reference to a named content model group (group), or an element wildcard (any). With a few exceptions, anywhere one type of particle is allowed, the other five are allowed as well. A complex type definition contains a sequence of particles that indicate which elements can appear in instances of that type. All of the local element declarations shown in the previous section were particles ...