+This module has a procedural interface (used to hash an entire
+message) and an OO interface (used to hash a message bit by bit). The
+procedural interface is made of three functions, all exported by
+default:
+
+=over
+
+=item B<highway_hash64> I<\@key>, I<$input>
+
+Compute the 64-bit HighwayHash of I<$input>, using I<\@key> as a key.
+The key must be a 4-element arrayref, with each element either a
+number or (on Perls without 64-bit numbers) a L<Math::Int64> object. The result is a single number or (on Perls without 64-bit numbers) a L<Math::Int64> object.
+
+=item B<highway_hash128> I<\@key>, I<$input>
+
+Compute the 128-bit HighwayHash of I<$input>, using I<\@key> as a key.
+The key must be a 4-element arrayref, with each element either a
+number or (on Perls without 64-bit numbers) a L<Math::Int64> object. The result is an array of exactly two numbers or (on Perls without 64-bit numbers) L<Math::Int64> objects.
+
+=item B<highway_hash256> I<\@key>, I<$input>
+
+Compute the 256-bit HighwayHash of I<$input>, using I<\@key> as a key.
+The key must be a 4-element arrayref, with each element either a
+number or (on Perls without 64-bit numbers) a L<Math::Int64> object. The result is an array of exactly four numbers or (on Perls without 64-bit numbers) L<Math::Int64> objects.
+
+
+=back
+
+The OO interface has these methods:
+
+=over
+
+=item Digest::HighwayHash->B<new>(I<\@key>)
+
+Initialize a new C<Digest::HighwayHash> state with a given key. The
+B<append> method will be called with this state and parts of the
+message, and then one of the B<finish*> methods will be called to
+compute the result.
+
+=item $state->B<append>(I<$input>)
+
+Append I<$input> to the message to be hashed by $state.
+
+=item $state->B<finish64>
+
+=item $state->B<finish128>
+
+=item $state->B<finish256>
+
+Compute and return the 64-bit, 128-bit, or respectively 256-bit
+HighwayHash of this state. The return values are the same as in the
+procedural interface.
+
+=back
+