An R object may have a class attribute that is a character
  vector giving the names of classes it inherits from. stripClass
  strips the class classString from that character vector.
  stripTis(x) is shorthand for stripClass(x, "tis").
stripClass(x, classString)
stripTis(x)an object whose class character vector may or may not
	include classString
name of class to remove from the inheritance chain
An object like x, but whose class attribute does
  not include classString.  If the class attribute less
  classString is empty, unclass(x) is returned.