diff --git a/setools/policyrep/constraint.py b/setools/policyrep/constraint.py
index be7e5c1..d2fead7 100644
--- a/setools/policyrep/constraint.py
+++ b/setools/policyrep/constraint.py
@@ -228,6 +228,8 @@ class BaseConstraint(symbol.PolicySymbol):
 
 class Constraint(BaseConstraint):
 
+    """A constraint rule (constrain/mlsconstrain)."""
+
     def __str__(self):
         rule_string = "{0.ruletype} {0.tclass} ".format(self)
 
@@ -250,5 +252,7 @@ class Constraint(BaseConstraint):
 
 class Validatetrans(BaseConstraint):
 
+    """A validatetrans rule (validatetrans/mlsvalidatetrans)."""
+
     def __str__(self):
         return "{0.ruletype} {0.tclass}\n\t{1}\n);".format(self, self._build_expression())