+\end{code}
+
+
+%************************************************************************
+%* *
+ The ABI of an IfaceDecl
+%* *
+%************************************************************************
+
+Note [The ABI of an IfaceDecl]
+~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
+The ABI of a declaration consists of:
+
+ (a) the full name of the identifier (inc. module and package,
+ because these are used to construct the symbol name by which
+ the identifier is known externally).
+
+ (b) the declaration itself, as exposed to clients. That is, the
+ definition of an Id is included in the fingerprint only if
+ it is made available as as unfolding in the interface.
+
+ (c) the fixity of the identifier
+ (d) for Ids: rules
+ (e) for classes: instances, fixity & rules for methods
+ (f) for datatypes: instances, fixity & rules for constrs
+
+Items (c)-(f) are not stored in the IfaceDecl, but instead appear
+elsewhere in the interface file. But they are *fingerprinted* with
+the Id itself. This is done by grouping (c)-(f) in IfaceDeclExtras,
+and fingerprinting that as part of the Id.