A model group is used to define an element that has mixed content or element content. |
A model group is bounded by brackets, and contains at least one token. |
When a model group contains more than one content token, the child elements are controlled using two logical connector operators; sequence connector `,', and choice connector `|' |
<!ELEMENT element1 (a, b, c)> indicates a is followed by element b, which in turn is followed by c. |
<!ELEMENT element2 (a | b | c)> indicates either one can be selected. |
Combinations are possible: (a,b,(c|d)), or ((a,b,c) | d) |