Set of special type definitions. Each defines a method for getting a test value and a method for getting a string representation of the value.
Example:
// special Date type may looks like
{
constr: Date, // constructor method
value: function(val) { return val.getTime(); }, // returns a value for testing instead of original value
caption: function(val) { return 'Date("' + val.toLocaleString() + '")'; } // returns a text for reporting
}