shapelib-toml: Add an internal comment

Signed-off-by: Ian Jackson <ijackson@chiark.greenend.org.uk>

diff --git a/src/shapelib-toml.rs b/src/shapelib-toml.rs
index 4b03ba9dbb227a8ab3f9a65888d8bbff60ef4569..b57362925f34ff8e76dad5292d0f78253b8c119b 100644 (file)
--- a/src/shapelib-toml.rs
+++ b/src/shapelib-toml.rs
@@ -48,6 +48,10 @@ pub struct LibraryTomlFile {
 /// implementation convenient (for complicated reasons).  At the
 /// library TOML file level, there is no meaningful difference between
 /// the fields in this struct, and the ones in `GroupDetails`
+//
+// At the implementation level, each loaded item contains an
+// `Arc<GroupDetails>`, which is simply stored directly.  The
+// `GroupDefn` is processed.
 #[derive(Debug,Deserialize)]
 pub struct GroupDefn {
   /// `files` is a multi-line string, each line of which has three