Provide documentation for the deprecated_features XML attribute.
Available since 11.0.0, and supported for S390.

Signed-off-by: Collin Walling <walling@linux.ibm.com>
---
 docs/formatdomain.rst | 8 ++++++++
 1 file changed, 8 insertions(+)

diff --git a/docs/formatdomain.rst b/docs/formatdomain.rst
index c7c75ae219..fbe8da765f 100644
--- a/docs/formatdomain.rst
+++ b/docs/formatdomain.rst
@@ -1674,6 +1674,14 @@ In case no restrictions need to be put on CPU model and its features, a simpler
       </cpu>
       ...
 
+``deprecated_features``
+   :since:`Since 11.0.0`, S390 guests may utilize the ``deprecated_features``
+   attribute to specify toggling of CPU model features that are flagged as
+   deprecated by the hypervisor. When this attribute is set to ``off``, the
+   active guest XML will reflect the respective features with the disable
+   policy. When this attribute is set to ``on``, the respective features will
+   be enabled.
+
 ``cache``
    :since:`Since 3.3.0` the ``cache`` element describes the virtual CPU cache.
    If the element is missing, the hypervisor will use a sensible default.
-- 
2.47.1