Description:
------------
User-contributed notes and my own limited experience indicates that 0 and 1 are "special" to the chunk_size in ob_start() and make the callback not behave as documented.

Can this be documented?

Or was it a bug that got fixed?


Reproduce code:
---------------
<?php
  //abuses ob_start callback in CLI to 'tee' output
  //to both buffer and stderr
  function tee($string){
    error_log($string);
    return false;
  }
  ob_start('tee', 0); //fails
  ob_start('tee', 1); //fails
  ob_start('tee', 2); //works!
?>


Expected result:
----------------
0, 1, and 2 should behave the same, or be documented as special.