Using Constraints

Web<ToolKit> uses a rule set to handle os_element_group derived class constraints. When constraint checking is enabled, the contents of an element group are checked against the rule set. Constraint checking occurs when the element group is converted to HTML when either print() or operator<< is called, not when elements are added to the element group. By default, constraint checking is disabled.

If, during constraint checking, an element in an element group is found to be in violation of the constraint rules for that group, the element is not printed. Instead, a constraint violation message is sent to the output stream.

The advantages of constraint checking are two-fold.

Explicitly identifies what is invalid on a Web page. This is very helpful during program testing.
Allows consistent, understandable display, no matter which Web browser is used.

This section provides a brief overview of the constraint rule set, as well as examples of how a constraint violation is handled when constraint checking is either enabled or disabled.

Using Constraints

The Constraint Rule Set

Constraint Checking