The Constraint Rule Set

The use of a constraint rule set for element groups provides a flexible structure for validating elements contained in Web<ToolKit> element group classes.

The constraint rule set identifies the elements that an os_element_group derived class can contain. When constraint checking is enabled, the elements in an element group are verified according to these rules when the page is converted to HTML. If an element is in violation of constraint rules, a message naming the illegal element and the element group is printed.

Assume an os_list_item is added to an os_table . This is a constraint violation because os_table can only contain one type of element, os_table_row .

If constraint checking is enabled when this violation is encountered, a constraint violation message is rendered. The output process is not stopped. This message is visible when the Web page is viewed in a Web browser.



Constraint Violation: os_table cannot contain an os_list_item element.

The message is always displayed in the above format with the name of the element group class and the violating element in a fixed-width font.

If constraint checking is disabled when the above violation is encountered, no action is taken. The table is rendered containing a list item, in violation of HTML standards. How this violation is handled depends upon the browser being used.