ref-manual/variables.rst: document the REQUIRED_IMAGE_FEATURES variable

Added by commit 96a9702a24a7 ("distro_features_check: expand with
IMAGE_FEATURES") in OE-Core.

Reviewed-by: Quentin Schulz <quentin.schulz@cherry.de>
(From yocto-docs rev: 860ddbd491ee9db291868bd939392538a2c64a4b)

Signed-off-by: Antonin Godard <antonin.godard@bootlin.com>
Signed-off-by: Richard Purdie <richard.purdie@linuxfoundation.org>

1 files changed, 17 insertions, 0 deletions

diff --git a/documentation/ref-manual/variables.rst b/documentation/ref-manual/variables.rst
index 33da2286b3..cd55bf13b1 100644
--- a/documentation/ref-manual/variables.rst
+++ b/documentation/ref-manual/variables.rst
@@ -7960,6 +7960,23 @@ system and gives an overview of their function and contents.
       the recipe will be skipped, and if the build system attempts to build
       the recipe then an error will be triggered.
 
+   :term:`REQUIRED_IMAGE_FEATURES`
+      When inheriting the :ref:`ref-classes-features_check` class, this variable
+      identifies image features that must exist in the current
+      configuration in order for the :term:`OpenEmbedded Build System` to build
+      the recipe. In other words, if the :term:`REQUIRED_IMAGE_FEATURES` variable
+      lists a feature that does not appear in :term:`IMAGE_FEATURES` within the
+      current configuration, then the recipe will be skipped, and if the build
+      system attempts to build the recipe then an error will be triggered.
+
+      Compared to other ``REQUIRED_*_FEATURES`` variables, the
+      :term:`REQUIRED_IMAGE_FEATURES` varible only targets image recipes, as the
+      :term:`IMAGE_FEATURES` variable is handled by the :ref:`ref-classes-core-image`
+      class). However, the :term:`REQUIRED_IMAGE_FEATURES` varible can also be
+      set from a :term:`Configuration File`, such as a distro
+      configuration file, if the list of required image features should apply to
+      all images using this :term:`DISTRO`.
+
    :term:`REQUIRED_MACHINE_FEATURES`
       When inheriting the :ref:`ref-classes-features_check` class, this variable
       identifies :term:`MACHINE_FEATURES` that must exist in the current