any number of bar1, bar2, and bar3 elements in any order
<!ELEMENT Foo (bar1|bar2|bar3)>
one child element, either bar1, bar2, or bar3
><!ELEMENT Foo (bar1, bar2, bar3)*>
0 or more bar1, bar2, bar3 sequences.
><!ELEMENT Foo (bar1?, bar2?, bar3?)>
any of:
bar1
bar2
bar3
bar1 bar2
bar1 bar3
bar2 bar3
bar1 bar2 bar3
I agree that the semantic of '|' is not as it is in some other
systems. -T.