Update docs

1 files changed, 7 insertions, 0 deletions

diff --git a/src/cell.h b/src/cell.h
index 09d9144d..84948fb4 100644
--- a/src/cell.h
+++ b/src/cell.h
@@ -26,6 +26,13 @@ struct rvec
 	double   w;
 };
 
+
+/**
+ * UnitCell:
+ *
+ * This data structure is opaque.  You must use the available accessor functions
+ * to read and write its contents.
+ **/
 typedef struct _unitcell UnitCell;
 
 extern UnitCell *cell_new(void);