diff --git a/Makefile b/Makefile
index 334757f5..8218448b 100644
--- a/Makefile
+++ b/Makefile
@@ -49,6 +49,9 @@ $(SUBDIRS):
 test:
 	cargo test $(CARGO_BUILD_ARGS)
 
+doc:
+	cargo doc $(CARGO_BUILD_ARGS)
+
 # always re-create this dir
 # but also copy the local target/ dir as a build-cache
 .PHONY: build
diff --git a/src/backup.rs b/src/backup.rs
index e38cb194..5a4a4981 100644
--- a/src/backup.rs
+++ b/src/backup.rs
@@ -1,4 +1,15 @@
-//! This mudule implements the proxmox backup chunked data storage
+//! This module implements the proxmox backup chunked data storage
+//!
+//! A chunk is simply defined as binary blob. We store them inside a
+//! `ChunkStore`, addressed by the SHA256 digest of the binary
+//! blob. This technology is also known as content-addressable
+//! storage.
+//!
+//! We store larger files by splitting them into chunks. The resulting
+//! SHA256 digest list is stored as separate index file. The
+//! `DynamicIndex*` format is able to deal with dynamic chunk sizes,
+//! whereas the `FixedIndex*` format is an optimization to store a
+//! list of equal sized chunks.
 
 pub mod chunker;
 pub mod chunk_store;