Update doc comments.

Author: m-ou-se

library/proc_macro/src/lib.rs

@@ -543,13 +543,13 @@ impl Span {
     /// The path to the source file in which this span occurs, for display purposes.
     ///
     /// This might not correspond to a valid file system path.
-    /// It might be remapped, or might be an artificial path such as `"<macro expansion>"`.
+    /// It might be remapped (e.g. `"/src/lib.rs"`) or an artificial path (e.g. `"<command line>"`).
     #[stable(feature = "proc_macro_span_file", since = "CURRENT_RUSTC_VERSION")]
     pub fn file(&self) -> String {
         self.0.file()
     }
 
-    /// The path to the source file in which this span occurs on disk.
+    /// The path to the source file in which this span occurs on the local file system.
     ///
     /// This is the actual path on disk. It is unaffected by path remapping.
     ///