added explanation of variables' scope within {include}

docs/en/designers/language-builtin-functions/language-function-include.xml

@@ -14,7 +14,13 @@
   {include} will be assigned to instead of
   displayed.
  </para>
- 
+ <para>
+  All assigned variables' values are restored after the scope of the
+  included template is left. This means you can use all variables from
+  the including template inside the included template. But changes to
+  variables inside the included template are not visible inside the
+  including template after the {include} statement.
+ </para>
  <informaltable frame="all">
   <tgroup cols="5">
    <colspec colname="param" align="center" />