Improve comments for FFI_ExecuteNamedAction.

Change-Id: I5be1aa6333e6b02a60962c3466288f6d0dc0173d
Reviewed-on: https://pdfium-review.googlesource.com/c/pdfium/+/93310
Commit-Queue: Tom Sepez <tsepez@chromium.org>
Reviewed-by: Lei Zhang <thestig@chromium.org>
diff --git a/public/fpdf_formfill.h b/public/fpdf_formfill.h
index 03305e0..0cafb9a 100644
--- a/public/fpdf_formfill.h
+++ b/public/fpdf_formfill.h
@@ -637,8 +637,9 @@
    * Return value:
    *       None.
    * Comments:
-   *       See the named actions description of <<PDF Reference, version 1.7>>
-   *       for more details.
+   *       See ISO 32000-1:2008, section 12.6.4.11 for descriptions of the
+   *       standard named actions, but note that a document may supply any
+   *       name of its choosing.
    */
   void (*FFI_ExecuteNamedAction)(struct _FPDF_FORMFILLINFO* pThis,
                                  FPDF_BYTESTRING namedAction);