DEFVAR_LISP ("undo-outer-limit", &Vundo_outer_limit,
doc: /* Outer limit on size of undo information for one command.
At garbage collection time, if the current command has produced
-more than this much undo information, it asks you whether to delete
-the information. This is a last-ditch limit to prevent memory overflow.
+more than this much undo information, it discards the info and displays
+a warning. This is a last-ditch limit to prevent memory overflow.
-The size is counted as the number of bytes occupied,
-which includes both saved text and other data.
+The size is counted as the number of bytes occupied, which includes
+both saved text and other data. A value of nil means no limit. In
+this case, accumulating one huge undo entry could make Emacs crash as
+a result of memory overflow.
In fact, this calls the function which is the value of
`undo-outer-limit-function' with one argument, the size.