Help/dev/experimental: Link to published P1689R4

Help/dev/experimental.rst

@@ -39,13 +39,7 @@ to the file specified by the ``<DEP_FILE>`` placeholder, and write module
 dependencies to the file specified by the ``<DYNDEP_FILE>`` placeholder.
 
 The module dependencies should be written in the format described
-by the `P1689r3`_ paper, with the following updates:
-
-* Omit the ``outputs``, ``inputs``, and ``depends`` fields from
-  each entry in the ``rules`` array.  They are unused.
-* Flatten ``future-compile`` members directly into each rule.
-* Factor a ``primary-output`` field out of the now-flattened ``outputs``.
-* The ``work-directory`` field is optional.
+by the `P1689r4`_ paper.
 
 Compiler writers may try out their scanning functionality using
 the `cxx-modules-sandbox`_ test project, modified to set variables
@@ -72,5 +66,5 @@ the GCC documentation, but the relevant section for the purposes of CMake is:
     -- GCC module mapper documentation
 
 .. _`D1483r1`: https://mathstuf.fedorapeople.org/fortran-modules/fortran-modules.html
-.. _`P1689r3`: http://www.open-std.org/jtc1/sc22/wg21/docs/papers/2020/p1689r3.html
+.. _`P1689r4`: http://www.open-std.org/jtc1/sc22/wg21/docs/papers/2021/p1689r4.html
 .. _`cxx-modules-sandbox`: https://github.com/mathstuf/cxx-modules-sandbox