How WinRunner handles varying window labels?

We can handle varying window labels using regular expressions. WinRunner uses two hidden properties in order to use regular expression in an object’s physical description. These properties are regexp_label and regexp_MSW_class.
i. The regexp_label property is used for windows only. It operates behind the scenes to insert a regular expression into a window’s label description.
ii. The regexp_MSW_class property inserts a regular expression into an object’s MSW_class. It is obligatory for all types of windows and for the object class object.