[gnome-continuous-yocto/gnomeostree-3.28-rocko: 1338/8267] ref-manual: Added clarifying note to the BBCLASSEXTEND variable.

[Emmanuele Bassi <ebassi src gnome org>]

commit 640181cce81663b0a2055592382d127eac5d63ba
Author: Scott Rifenbark <srifenbark gmail com>
Date:   Tue Jul 12 14:10:13 2016 -0700

    ref-manual: Added clarifying note to the BBCLASSEXTEND variable.
    
    Fixes [YOCTO #9909]
    
    Added a note that talks about how the BBCLASSEXTEND mechanism
    adds recipe variants.
    
    (From yocto-docs rev: a05990ecb760519a685a1c5ddcf2ce3e048bfbf2)
    
    Signed-off-by: Scott Rifenbark <srifenbark gmail com>
    Signed-off-by: Richard Purdie <richard purdie linuxfoundation org>

 documentation/ref-manual/ref-variables.xml |   21 +++++++++++++++++++++
 1 files changed, 21 insertions(+), 0 deletions(-)
---
diff --git a/documentation/ref-manual/ref-variables.xml b/documentation/ref-manual/ref-variables.xml
index 3278ccc..b876bc3 100644
--- a/documentation/ref-manual/ref-variables.xml
+++ b/documentation/ref-manual/ref-variables.xml
@@ -995,6 +995,27 @@
      BBCLASSEXTEND =+ "native nativesdk"
      BBCLASSEXTEND =+ "multilib:<replaceable>multilib_name</replaceable>"
                     </literallayout>
+                    <note>
+                        <para>
+                        Internally, the <filename>BBCLASSEXTEND</filename>
+                        mechanism generates recipe variants by rewriting
+                        variable values and applying overrides such as
+                        <filename>_class-native</filename>.
+                        For example, to generate a native version of a recipe
+                        named "foo", a
+                        <link linkend='var-DEPENDS'><filename>DEPENDS</filename></link>
+                        on "foo" is rewritten to a <filename>DEPENDS</filename>
+                        on "foo-native".
+                        </para>
+
+                        <para>
+                        No reparsing, which adds some limitations, of the
+                        recipe is done for each variant.
+                        For example, it is not possible to "include" a
+                        different file depending on the variant, since
+                        "include's" are processed when the recipe is parsed.
+                        </para>
+                    </note>
                 </para>
              </glossdef>
         </glossentry>