Update docs

1 files changed, 7 insertions, 2 deletions

diff --git a/src/symmetry.h b/src/symmetry.h
index c91864bb..071ebbde 100644
--- a/src/symmetry.h
+++ b/src/symmetry.h
@@ -20,14 +20,19 @@
 /**
  * SymOpList
  *
- * Opaque type.
+ * The SymOpList is an opaque data structure containing a list of point symmetry
+ * operations.  It could represent an point group or a list of indexing
+ * ambiguities (twin laws), or similar.
  **/
 typedef struct _symoplist SymOpList;
 
 /**
  * SymOpMask
  *
- * Opaque type.
+ * The SymOpMask is an opaque data structure containing a list of flags
+ * associated with point symmetry operations in a specific %SymOpList.  It is
+ * used to filter the operations in the %SymOpList to avoid duplicating
+ * equivalent reflections when the reflection is somehow special (e.g. 'hk0').
  **/
 typedef struct _symopmask SymOpMask;