diff --git a/src/libcore/hashmap.rs b/src/libcore/hashmap.rs
index 7d9320b9b0f93..472de88f692b8 100644
--- a/src/libcore/hashmap.rs
+++ b/src/libcore/hashmap.rs
@@ -8,7 +8,10 @@
 // option. This file may not be copied, modified, or distributed
 // except according to those terms.
 
-//! Sendable hash maps.
+//! An unordered map and set type implemented as hash tables
+//!
+//! The tables use a keyed hash with new random keys generated for each container, so the ordering
+//! of a set of keys in a hash table is randomized.
 
 /// Open addressing with linear probing.
 pub mod linear {
diff --git a/src/libcore/ops.rs b/src/libcore/ops.rs
index 2f7fe1e4aa8bf..4d17fb2f69640 100644
--- a/src/libcore/ops.rs
+++ b/src/libcore/ops.rs
@@ -8,7 +8,7 @@
 // option. This file may not be copied, modified, or distributed
 // except according to those terms.
 
-// Core operators
+//! Traits for the built-in operators
 
 #[lang="drop"]
 pub trait Drop {
diff --git a/src/libstd/base64.rs b/src/libstd/base64.rs
index cdc15ae1d45dc..d3452712728b9 100644
--- a/src/libstd/base64.rs
+++ b/src/libstd/base64.rs
@@ -8,6 +8,8 @@
 // option. This file may not be copied, modified, or distributed
 // except according to those terms.
 
+//! Base64 binary-to-text encoding
+
 use core::iter;
 use core::str;
 use core::vec;