- /// Specifies what nested things a visitor wants to visit. The most
- /// common choice is `OnlyBodies`, which will cause the visitor to
- /// visit fn bodies for fns that it encounters, but skip over nested
- /// item-like things.
+ /// Specifies what nested things a visitor wants to visit. By "nested
+ /// things", we are referring to bits of HIR that are not directly embedded
+ /// within one another but rather indirectly, through a table in the crate.
+ /// This is done to control dependencies during incremental compilation: the
+ /// non-inline bits of HIR can be tracked and hashed separately.
+ ///
+ /// The most common choice is `OnlyBodies`, which will cause the visitor to
+ /// visit fn bodies for fns that it encounters, and closure bodies, but
+ /// skip over nested item-like things.