diff --git a/library/core/src/macros/mod.rs b/library/core/src/macros/mod.rs
index 771c2d31b60e0..a25b631b9bd21 100644
--- a/library/core/src/macros/mod.rs
+++ b/library/core/src/macros/mod.rs
@@ -1287,13 +1287,19 @@ pub(crate) mod builtin {
 
     /// Expands to the file name in which it was invoked.
     ///
-    /// With [`line!`] and [`column!`], these macros provide debugging information for
-    /// developers about the location within the source.
-    ///
-    /// The expanded expression has type `&'static str`, and the returned file
-    /// is not the invocation of the `file!` macro itself, but rather the
-    /// first macro invocation leading up to the invocation of the `file!`
-    /// macro.
+    /// With [`line!`] and [`column!`], these macros provide debugging information for developers
+    /// about the location within the source.
+    ///
+    /// The expanded expression has type `&'static str`, and the returned file is not the invocation
+    /// of the `file!` macro itself, but rather the first macro invocation leading up to the
+    /// invocation of the `file!` macro.
+    ///
+    /// The file name is derived from the root module's source path passed to the Rust compiler
+    /// (e.g. `./src/lib.rs`) and the sequence the compiler takes to get from root module to the
+    /// module containing `file!` (e.g. inside `mod foo;` in `./src/lib.rs`, `file!` would be
+    /// `./src/foo.rs`), modified by any flags passed to the Rust compiler (e.g.
+    /// `--remap-path-prefix`).  If the source path is relative, the initial base directory will be
+    /// the working directory of the Rust compiler.
     ///
     /// # Examples
     ///