// FindReaderIndex returns a two-element slice of integers defining the
// location of the leftmost match of the regular expression in text read from
-// the RuneReader. The match itself is at s[loc[0]:loc[1]]. A return
-// value of nil indicates no match.
+// the RuneReader. The match text was found in the input stream at
+// byte offset loc[0] through loc[1]-1.
+// A return value of nil indicates no match.
func (re *Regexp) FindReaderIndex(r io.RuneReader) (loc []int) {
a := re.doExecute(r, nil, "", 0, 2)
if a == nil {