Update documentation about box-decoration-break and margin-break

Fix #771.

docs/features.rst

@@ -547,21 +547,28 @@ that should be efficient with simple cases.
 .. _CSS Multi-column Layout Module: https://www.w3.org/TR/css3-multicol/
 
 
-CSS Fragmentation Module Level 3
-~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
+CSS Fragmentation Module Level 3 / 4
+~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
 
 The `CSS Fragmentation Module Level 3`_ "describes the fragmentation model that
 partitions a flow into pages, columns, or regions. It builds on the Page model
 module and introduces and defines the fragmentation model. It adds
 functionality for pagination, breaking variable fragment size and orientation,
 widows and orphans."
 
+The `CSS Fragment Module Level 4`_ is a working draft on the same subject.
+
 The ``break-before``, ``break-after`` and ``break-inside`` properties are
 supported for pages, but **not** for columns and regions. ``page-break-*``
 aliases as defined in CSS2 are supported too.
 
 The ``orphans`` and ``widows`` properties are supported.
 
-The ``box-decoration-break`` property is **not** supported.
+The ``box-decoration-break`` property is supported, but backgrounds are always
+repeated and not extended through the whole box as it should be with 'slice'
+value.
+
+The ``margin-break`` property is supported.
 
 .. _CSS Fragmentation Module Level 3: https://www.w3.org/TR/css-break-3/
+.. _CSS Fragmentation Module Level 4: https://www.w3.org/TR/css-break-4/