+TRelativeJobId = WithDesc("RelativeJobId")(TNegativeInt)
+
+
+def TInstanceOf(cls):
+ """Checks if a given value is an instance of C{cls}.
+
+ @type cls: class
+ @param cls: Class object
+
+ """
+ name = "%s.%s" % (cls.__module__, cls.__name__)
+
+ desc = WithDesc("Instance of %s" % (Parens(name), ))
+
+ return desc(lambda val: isinstance(val, cls))