Modified documentation for `org-src-preserve-indentation'

TINYCHANGE

doc/org.texi

@@ -13781,8 +13781,13 @@ can be used to map arbitrary language names to existing major modes.
 @item org-src-window-setup
 Controls the way Emacs windows are rearranged when the edit buffer is created.
 @item org-src-preserve-indentation
-This variable is especially useful for tangling languages such as
-Python, in which whitespace indentation in the output is critical.
+By default, the value is @code{nil}, which means that when code blocks are
+evaluated during export or tangled, they are re-inserted into the code block,
+which may replace sequences of spaces with tab characters.  When non-nil,
+whitespace in code blocks will be preserved during export or tangling,
+exactly as it appears.  This variable is especially useful for tangling
+languages such as Python, in which whitespace indentation in the output is
+critical.
 @item org-src-ask-before-returning-to-edit-buffer
 By default, Org will ask before returning to an open edit buffer.  Set this
 variable to @code{nil} to switch without asking.