Document Interval::delta().

diff --git a/flower/include/interval.hh b/flower/include/interval.hh
index 9c831816c439661856fb240c07d61b4bdad03a96..be7074c242bec76dc2a599e4e9359e6ad9e73556 100644 (file)
--- a/flower/include/interval.hh
+++ b/flower/include/interval.hh
@@ -68,6 +68,8 @@ struct Interval_t : public Drul_array<T>
     at (RIGHT) = max (at (RIGHT), p);
   }
   T length () const;
+
+  // Returns RIGHT - LEFT, even if the interval is empty.
   T delta () const;
   void set_empty ();
   void set_full ();