anchor.diff:    mkNotdef = {_type = "notdef";};
   
     # General property type, it has a property attribute and a content
  -  # attribute.  The property attribute refer to an attribute set which
  +  # attribute.  The property attribute refers to an attribute set which
     # contains a _type attribute and a list of functions which are used to
  -  # evaluate this property.  The content attribute is used to stack property
  +  # evaluate this property.  The content attribute is used to stack properties
     # on top of each other.
     # 
     # The optional functions which may be contained in the property attribute
  
positive.code:       content = mkNotdef;
      };
  
    # Create an "Always" property remove ignore all "If" statement.
    isAlways = attrs: (typeOf attrs) == "always";
    mkAlways = value:
      mkProperty {
  
negative.code:     inherit content;
    };
  
    # Create a "ThenElse" property which contains choices being chosen by
    # the evaluation of an "If" statement.
    isThenElse = attrs: (typeOf attrs) == "then-else";
    mkThenElse = attrs:
  