Help: clarify range for list(INSERT), mention nonexistent / empty case

Help/command/list.rst

@@ -152,7 +152,12 @@ For more information on regular expressions look under
 
   list(INSERT <list> <element_index> <element> [<element> ...])
 
-Inserts elements to the list to the specified index.
+Inserts elements to the list to the specified index. It is an
+error to specify an out-of-range index. Valid indexes are 0 to `N`
+where `N` is the length of the list, inclusive. An empty list
+has length 0. If no variable named ``<list>`` exists in the
+current scope its value is treated as empty and the elements are
+inserted in that empty list.
 
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