-(defun split-string (string &optional separators)
- "Splits STRING into substrings where there are matches for SEPARATORS.
-Each match for SEPARATORS is a splitting point.
-The substrings between the splitting points are made into a list
+(defconst split-string-default-separators "[ \f\t\n\r\v]+"
+ "The default value of separators for `split-string'.
+
+A regexp matching strings of whitespace. May be locale-dependent
+\(as yet unimplemented). Should not match non-breaking spaces.
+
+Warning: binding this to a different value and using it as default is
+likely to have undesired semantics.")
+
+;; The specification says that if both SEPARATORS and OMIT-NULLS are
+;; defaulted, OMIT-NULLS should be treated as t. Simplifying the logical
+;; expression leads to the equivalent implementation that if SEPARATORS
+;; is defaulted, OMIT-NULLS is treated as t.
+(defun split-string (string &optional separators omit-nulls)
+ "Splits STRING into substrings bounded by matches for SEPARATORS.
+
+The beginning and end of STRING, and each match for SEPARATORS, are
+splitting points. The substrings matching SEPARATORS are removed, and
+the substrings between the splitting points are collected as a list,