(PECL event >= 1.6.0)
EventBuffer::substr — Substracts a portion of the buffer data
$start
   
   [, 
    int
     $length
   
  ] )
   Substracts up to
   length
   bytes of the buffer data beginning at
   start
   position.
  
start
    The start position of data to be substracted.
length
    Maximum number of bytes to substract.
   Returns the data substracted as a
   string
   on success, or FALSE on failure.