Merge pull request #2218 from Xliff/xliff-patch-20180725

Xliff patch 20180725

doc/Type/Str.pod6

@@ -1042,12 +1042,13 @@ Also using a different value or an incorrect starting index won't match:
 
 =head2 method substr-rw
 
-    method substr-rw($from, $length?)
+    method substr-rw($from, $length = *)
 
 A version of C<substr> that returns a L<Proxy|/type/Proxy> functioning as a
 writable reference to a part of a string variable. Its first argument, C<$from>
 specifies the index in the string from which a substitution should occur, and
 its last argument, C<$length> specifies how many characters are to be replaced.
+If not specified, C<$length> defaults to the length of the string.
 
 For example, in its method form, if one wants to take the string C<"abc">
 and replace the second character (at index 1) with the letter C<"z">, then