--- a/mobile/android/base/java/org/mozilla/gecko/reader/ReaderModeUtils.java
+++ b/mobile/android/base/java/org/mozilla/gecko/reader/ReaderModeUtils.java
@@ -7,16 +7,24 @@ package org.mozilla.gecko.reader;
 import org.mozilla.gecko.AboutPages;
 import org.mozilla.gecko.util.StringUtils;
 
 import android.net.Uri;
 
 public class ReaderModeUtils {
     private static final String LOGTAG = "ReaderModeUtils";
 
+    /**
+     * Extract the URL from a valid about:reader URL. You may want to use stripAboutReaderUrl
+     * instead to always obtain a valid String.
+     *
+     * @see #stripAboutReaderUrl(String) for a safer version that returns the original URL for malformed/invalid
+     *     URLs.
+     * @return <code>null</code> if the URL is malformed or doesn't contain a URL parameter.
+     */
     public static String getUrlFromAboutReader(String aboutReaderUrl) {
         return StringUtils.getQueryParameter(aboutReaderUrl, "url");
     }
 
     public static boolean isEnteringReaderMode(String currentUrl, String newUrl) {
         if (currentUrl == null || newUrl == null) {
             return false;
         }