Note on ASCII assumptions in content_max_width

src/display/side_by_side.rs

@@ -201,7 +201,10 @@ impl SourceDimensions {
         //
         // This is a crude heuristic because it ignores which lines of
         // the file actually get displayed, so we can still end up
-        // with some superfluous space
+        // with some superfluous space. It also naively assumes that
+        // byte length is the same display length, which is generally
+        // OK because byte length will tend to be larger than the
+        // display length.
         let display_width = min(terminal_width, (content_max_width + 4) * 2 + SPACER.len());
 
         assert!(