diff --git a/core/includes/file.inc b/core/includes/file.inc
index 3fcb38a4e4..bf9dcb63e0 100644
--- a/core/includes/file.inc
+++ b/core/includes/file.inc
@@ -428,12 +428,14 @@ function file_valid_uri($uri) {
  *
  * This is a powerful function that in many ways performs like an advanced
  * version of copy().
- * - Checks if $source and $destination are valid and readable/writable.
- * - If file already exists in $destination either the call will error out,
- *   replace the file or rename the file based on the $replace parameter.
- * - If the $source and $destination are equal, the behavior depends on the
- *   $replace parameter. FILE_EXISTS_REPLACE will error out. FILE_EXISTS_RENAME
- *   will rename the file until the $destination is unique.
+ * - If $source and $destination are valid and readable/writable, then only
+ *   performs copy operation.
+ * - If $source and $destination are equal, return false. Do not overwrite a
+ *   file with itself.
+ * - If file already exists in $destination, the behavior depends on the
+ *   $replace parameter. FILE_EXISTS_ERROR will error out,
+ *   FILE_EXISTS_REPLACE will replace the existing file, and FILE_EXISTS_RENAME
+ *   will assign a new unique name (@see file_create_filename()).
  * - Works around a PHP bug where copy() does not properly support streams if
  *   safe_mode or open_basedir are enabled.
  *   @see https://bugs.php.net/bug.php?id=60456