Clarify necessity for file path normalization

PiperOrigin-RevId: 971491679
Change-Id: I26c9eecc53904abbe457c10473b4cafb8331f229

src/tools/java/com/google/devtools/build/android/dexer/ZipEntryComparator.java

diff --git a/src/tools/java/com/google/devtools/build/android/dexer/ZipEntryComparator.java b/src/tools/java/com/google/devtools/build/android/dexer/ZipEntryComparator.java
index ab0b838..e17650d 100644
--- a/src/tools/java/com/google/devtools/build/android/dexer/ZipEntryComparator.java
+++ b/src/tools/java/com/google/devtools/build/android/dexer/ZipEntryComparator.java
@@ -42,9 +42,13 @@
    * @return {@code compareTo()}-style result
    */
   // Copied from com.android.dx.cf.direct.ClassPathOpener
+  // See
+  // https://cs.android.com/android/platform/superproject/+/android-latest-release:dalvik/dx/src/com/android/dx/cf/direct/ClassPathOpener.java;l=187-200;drc=9dbd802c8c96c3a66873bc600bc7d1374a1d08e5
   @VisibleForTesting
   static int compareClassNames(String a, String b) {
     // Ensure inner classes sort second
+    // The strings being sorted are filenames (e.g. MyThing$1.class, MyThing.class), so this
+    // normalization is necessary.
     a = a.replace('$', '0');
     b = b.replace('$', '0');