Description:
------------
str_split is only able to split a string in periodical substrings. I think, it's a good improvement to allow arrays as a second parameter to handle sequences. I wrote a patch for that: http://www.xarg.org/2009/12/php-hacking/

Reproduce code:
---------------
var_dump(str_split("0123456789abcdefwant to extract this?abcd", array(16, -4)));

var_dump(str_split("hello how are you?", array(0, 1, 6, 7, 9, -2, -1)));


Expected result:
----------------
array(3) {
  [0]=>
  string(16) "0123456789abcdef"
  [1]=>
  string(21) "want to extract this?"
  [2]=>
  string(4) "abcd"
}
array(7) {
  [0]=>
  string(1) "h"
  [1]=>
  string(5) "ello "
  [2]=>
  string(1) "h"
  [3]=>
  string(2) "ow"
  [4]=>
  string(7) " are yo"
  [5]=>
  string(1) "u"
  [6]=>
  string(1) "?"
}