Content Model Groups
XML Schema supports constraints on a group of elements. Grouping may occur within a complexType or within a standalone group element that is then referenced from within a complexType.
A complexType element or a group element may contain the following constraints:
*One or more choice elements. This element declares that the document may contain one, and only one, of the types listed in the choice.
*One or more sequence elements. This element requires that the document contain the content types specified in the sequence. The names and the order of the content types must match the order in which they appear in the sequence.
*An all element. The types specified in an all element may occur in any order. An all element cannot be combined with other elements. That is, an element that has an all element as a child may not have any other children.
Note that the all, sequence, and choice elements themselves may have any value for minOccurs and maxOccurs. The code that HydraExpress generates depends on the elements within the group and the value of the minOccurs and maxOccurs attributes.