diff --git a/runtime/doc/map.txt b/runtime/doc/map.txt
index 19797b2..e0c7106 100644
--- a/runtime/doc/map.txt
+++ b/runtime/doc/map.txt
@@ -971,13 +971,18 @@
 Xterm and a few other terminals can be put in a mode where keys with modifiers
 are sent with a special escape code.  Vim recognizes these codes and can then
 make a difference between CTRL-H and Backspace, even when Backspace sends the
-character 8.  And many more special keys.
+character 8.  And many more special keys, such as Tab and CTRL-I, which cannot
+be mapped separately otherwise.
 
 For xterm modifyOtherKeys is enabled in the builtin termcap entry.  If this is
 not used you can enable modifyOtherKeys with these lines in your vimrc: >
       let &t_TI = "\<Esc>[>4;2m"
       let &t_TE = "\<Esc>[>4;m"
 
+This sets modifyOtherKeys to level 2.  Note that modifyOtherKeys level 1 does
+not work.  Some terminals do not support level 2 and then send key codes that
+Vim will not be able to correctly recognize.
+
 In case the modifyOtherKeys mode causes problems you can disable it: >
       let &t_TI = ""
       let &t_TE = ""
@@ -1001,10 +1006,15 @@
 detected such an escape sequence use `:verbose map`, the first line will then
 show "Seen modifyOtherKeys: true" (possibly translated).
 
+This automatic detection depends on receiving an escape code starting with 
+"<1b>[27;".  This is the normal way xterm sends these key codes.  However, if
+the *formatOtherKeys* resource is set another form is used that is not
+recognized, therefore you must not set formatOtherKeys.
+
 A known side effect is that in Insert mode the raw escape sequence is inserted
 after the CTRL-V key.  This can be used to check whether modifyOtherKeys is
 enabled: In Insert mode type CTRL-SHIFT-V CTRL-V, if you get one byte then
-modifyOtherKeys is off, if you get <1b>27;5;118~ then it is on.
+modifyOtherKeys is off, if you get <1b>[27;5;118~ then it is on.
 
 When the 'esckeys' option is off, then modifyOtherKeys will be disabled in
 Insert mode to avoid every key with a modifier causing Insert mode to end.