documentation of `org-babel-tangle-named-block-combination'

* doc/org.texi (Extracting source code): Documentation of the new
  org-babel-tangle-named-block-combination variable.

doc/org.texi

@@ -11546,6 +11546,23 @@ Tangle the current file.  Bound to @kbd{C-c C-v t}.
 Choose a file to tangle.   Bound to @kbd{C-c C-v f}.
 @end table
 
+@subsubheading Variables
+@table @code
+@item org-babel-tangle-named-block-combination
+This variable controls the tangling of multiple code blocks with the same
+name.
+@table @code
+@item nil
+The default behavior.  Blocks with the same name are tangled as normal.
+@item append
+The bodies of all blocks of the same name are appended during tangling.
+@item first
+Only the body of the first block of any given name is kept during tangling.
+@item last
+Only the body of the last block of any given name is kept during tangling.
+@end table
+@end table
+
 @subsubheading Hooks
 @table @code
 @item org-babel-post-tangle-hook