Element (continued)
In the Element declaration, the following table lists the values that content_model Values can contain:

Value

Description

(child1,child2,..., child_n)

Declares that an element has a sequence of child elements. The following example indicates that the mail element has four child elements to, from, subject, and text that must appear in the order specified within the parentheses:
    <!ELEMENT mail (to, from, subject, text)>

(child1|child2|...|child_n)

Declares that an element can have any one of the child elements among the elements separated by the “|” symbol. The following example indicates an element called mail that can contain any one of the specified child elements to, from, subject, or text:
    <!ELEMENT mail (to | from | subject | text)>

(#PCDATA)

Declares that an element contains text that needs to be parsed. The following example indicates that the to element contains data that does not use any markup text and special symbols, and that it must be parsed:
    <!ELEMENT to (#PCDATA)>

EMPTY

Declares that the element does not contain any data or child elements. The following example indicates an element called BR, which does not contain any child elements or data:
    <!ELEMENT BR EMPTY>

ANY

Declares that any data is allowed within the element. This data can be text, child elements, or both. The following example indicates an element called UNIVERSAL_SET, which can contain any combination of text and child elements:
    <!ELEMENT UNIVERSAL_SET ANY>

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