+ "Add an abbreviation to abbrev table TABLE.
+TYPE is a string describing in English the kind of abbrev this will be
+(typically, \"global\" or \"mode-specific\"); this is used in
+prompting the user. ARG is the number of words in the expansion.
+
+Return the symbol that internally represents the new abbrev, or nil if
+the user declines to confirm redefining an existing abbrev."