javax.swing.text.html.parser.ContentModel
Element's content representation. That's unary or binary expression. Operands can be null (matched with null object), instance of Element, instance of ContentType. Valid operations can be unary operations (types): 1)'+' - (e+) - e must occur one or more times; 2)'*' - (e*) - e must occur zero or more times; 3)'?' - (e?) - e must occur zero or one time; 4)(0) - (e) - e must occur one time only and binary operations (types): 1)'|' - (e1|e2) means either e1 or e2 must occur, but not both; 2)',' - (e1,e2) means both A and B must occur, in that order; 3)'&' - (e1 & e2) means both e1 and e2 must occur, in any order (Operation interpretation corresponds to HTML 4.01 Specification (3.3.3)) As content model is using for dtd presentation here is some ambiguity what null object can be matched with. So null shouldn't be passed to constructor. No resursion is allowed. Content, next, type fields has the following limitation: 1) if type is one from {'+', '*', '?'} content hasn't to be null; 2) if type is one from {'|', ',', '&'} content and next have not to be null; 3) content can be null if and only if type is 0; 4) content can be null, instance of Element or instance of ContentModel; 5) type can be one from the following '*', '+', '?', '|', '&', ','.