-extern bool operator== (Color const & a, Color const & b);
-extern bool operator!= (Color const & a, Color const & b);
-extern std::ostream & operator<< (std::ostream & s, Color const & c);
+extern bool operator== (Colour const & a, Colour const & b);
+extern bool operator!= (Colour const & a, Colour const & b);
+extern std::ostream & operator<< (std::ostream & s, Colour const & c);
+
+typedef boost::function<void (NoteType, std::string)> NoteHandler;
+
+/** Maximum absolute difference between dcp::SubtitleString::aspect_adjust values that
+ * are considered equal.
+ */
+const float ASPECT_ADJUST_EPSILON = 1e-3;
+
+/** Maximum absolute difference between dcp::SubtitleString alignment values that
+ * are considered equal.
+ */
+const float ALIGN_EPSILON = 1e-3;