diff --git a/compiler/rustc_ast/src/tokenstream.rs b/compiler/rustc_ast/src/tokenstream.rs
index 1f69a7dc356..a92ef575777 100644
--- a/compiler/rustc_ast/src/tokenstream.rs
+++ b/compiler/rustc_ast/src/tokenstream.rs
@@ -269,11 +269,14 @@ fn attrs_and_tokens_to_token_trees(
 /// with its attributes.
 ///
 /// This is constructed during parsing when we need to capture
-/// tokens.
+/// tokens, for `cfg` and `cfg_attr` attributes.
 ///
 /// For example, `#[cfg(FALSE)] struct Foo {}` would
 /// have an `attrs` field containing the `#[cfg(FALSE)]` attr,
 /// and a `tokens` field storing the (unparsed) tokens `struct Foo {}`
+///
+/// The `cfg`/`cfg_attr` processing occurs in
+/// `StripUnconfigured::configure_tokens`.
 #[derive(Clone, Debug, Encodable, Decodable)]
 pub struct AttrsTarget {
     /// Attributes, both outer and inner.
diff --git a/compiler/rustc_expand/src/config.rs b/compiler/rustc_expand/src/config.rs
index 323cea1af4a..9da4aa84db5 100644
--- a/compiler/rustc_expand/src/config.rs
+++ b/compiler/rustc_expand/src/config.rs
@@ -187,6 +187,7 @@ fn can_skip(stream: &AttrTokenStream) -> bool {
             .iter()
             .filter_map(|tree| match tree.clone() {
                 AttrTokenTree::AttrsTarget(mut target) => {
+                    // Expand any `cfg_attr` attributes.
                     target.attrs.flat_map_in_place(|attr| self.process_cfg_attr(&attr));
 
                     if self.in_cfg(&target.attrs) {
@@ -195,6 +196,8 @@ fn can_skip(stream: &AttrTokenStream) -> bool {
                         );
                         Some(AttrTokenTree::AttrsTarget(target))
                     } else {
+                        // Remove the target if there's a `cfg` attribute and
+                        // the condition isn't satisfied.
                         None
                     }
                 }