Add docstring explaining whatw Attribute does

lib/ansible/playbook/attribute.py

@@ -24,6 +24,34 @@ from copy import deepcopy
 class Attribute:
 
     def __init__(self, isa=None, private=False, default=None, required=False, listof=None, priority=0, class_type=None, always_post_validate=False, inherit=True):
+    """
+    :class:`Attribute` specifies constraints for attributes of objects which
+    derive from playbook data.  The attributes of the object are basically
+    a schema for the yaml playbook.
+
+    :kwarg isa: The type of the attribute.  Allowable values are a string
+        representation of any yaml basic datatype, python class, or percent.
+        (Enforced at post-validation time).
+    :kwarg private: (not used)
+    :kwarg default: Default value if unspecified in the YAML document.
+    :kwarg required: Whether or not the YAML document must contain this field.
+        If the attribute is None when post-validated, an error will be raised.
+    :kwarg listof: If isa is set to "list", this can optionally be set to
+        ensure that all elements in the list are of the given type. Valid
+        values here are the same as those for isa.
+    :kwarg priority: The order in which the fields should be parsed. Generally
+        this does not need to be set, it is for rare situations where another
+        field depends on the fact that another field was parsed first.
+    :kwarg class_type: If isa is set to “class”, this can be optionally set to
+        a class (not a string name). The YAML data for this field will be
+        passed to the __init__ method of that class during post validation and
+        the field will be an instance of that class.
+    :kwarg always_post_validate: Controls whether a field should be post
+        validated or not (default: True).
+    :kwarg inherit: A boolean value, which controls whether the object
+        containing this field should attempt to inherit the value from its
+        parent object if the local value is None.
+        """
 
         self.isa = isa
         self.private = private