diff --git a/bitbake/doc/bitbake-user-manual/bitbake-user-manual-metadata.xml b/bitbake/doc/bitbake-user-manual/bitbake-user-manual-metadata.xml
index 199ab23095..a125ad332e 100644
--- a/bitbake/doc/bitbake-user-manual/bitbake-user-manual-metadata.xml
+++ b/bitbake/doc/bitbake-user-manual/bitbake-user-manual-metadata.xml
@@ -61,6 +61,78 @@
+
+ Modifying Existing Variables
+
+
+ Sometimes you need to modify existing variables.
+ Following are some cases where you might find you want to
+ modify an existing variable:
+
+
+ Customize a recipe that uses the variable.
+
+
+ Change a variable's default value used in a
+ *.bbclass file.
+
+
+ Change the variable in a *.bbappend
+ file to override the variable in the original recipe.
+
+
+ Change the variable in a configuration file so that the
+ value overrides an existing configuration.
+
+
+
+
+
+ Changing a variable value can sometimes depend on how the
+ value was originally assigned and also on the desired
+ intent of the change.
+ In particular, when you append a value to a variable that
+ has a default value, the resulting value might not be what
+ you expect.
+ In this case, the value you provide might replace the value
+ rather than append to the default value.
+
+
+
+ If after you have changed a variable's value and something
+ unexplained occurs, you can use BitBake to check the actual
+ value of the suspect variable.
+ You can make these checks for both configuration and recipe
+ level changes:
+
+
+ For configuration changes, use the following:
+
+ $ bitbake -e
+
+ This command displays variable values after the
+ configuration files (i.e. local.conf,
+ bblayers.conf,
+ bitbake.conf and so forth) have
+ been parsed.
+
+ Variables that are exported to the environment are
+ preceded by the string "export" in the command's
+ output.
+
+
+
+ For recipe changes, use the following:
+
+ $ bitbake recipe -e | grep VARIABLE="
+
+ This command checks to see if the variable actually
+ makes it into a specific recipe.
+
+
+
+
+