Elements can contain subelements. For example, the following file fragment defines the VSCLASS element.
<!ELEMENT VSCLASS (VARS?, VS*, QOSPARAMS?)>
The ELEMENT tag specifies that a VSCLASS element can contain VARS, VS, and QOSPARAMS elements in that order.
The following table shows how optional suffix characters of subelements determine the requirement rules or number of allowed occurrences for the subelements.
Table 2–1 Requirement Rules and Subelement Suffixes
Subelement Suffix |
Requirement Rule |
---|---|
element* |
Can contain zero or more of this subelement |
element? |
Can contain zero or one of this subelement |
element+ |
Must contain one or more of this subelement |
element (no suffix) |
Must contain only one of this subelement |
If an element cannot contain other elements, you see EMPTY or (#PCDATA) instead of a list of element names in parentheses.