什么是PHP中的低级别可选语句

Question

PHP版本：5.3.3

以下是示例：

<?php
    declare(ticks=1);
    // declare(ticks=2);
    function handler()
    {
        echo "handler called\n";
    }
    register_tick_function('handler');
    $a = 1;
    // Output: handler called\nhandler called\n 
?>

只要将var handler called\nhandler called\n指定为ticks或1，输出就会相同2。

以下是vld生成的操作码：

Finding entry points
Branch analysis from position: 0
Return found
filename:       /home/soooldier/Php/2.php
function name:  (null)
number of ops:  10
compiled vars:  !0 = $a
line     # *  op                           fetch          ext  return  operands
---------------------------------------------------------------------------------
   2     0  >   TICKS                                                    1
         1      TICKS                                                    1
   4     2      NOP                                                      
   7     3      TICKS                                                    1
   8     4      SEND_VAL                                                 'handler'
         5      DO_FCALL                                      1                  'register_tick_function'
         6      TICKS                                                    1
   9     7      ASSIGN                                                   !0, 1
         8      TICKS                                                    1
  10     9    > RETURN                                                   1

branch: #  0; line:     2-   10; sop:     0; eop:     9
path #1: 0, 
Function handler:
Finding entry points
Branch analysis from position: 0
Return found
filename:       /home/soooldier/Php/2.php
function name:  handler
number of ops:  3
compiled vars:  none
line     # *  op                           fetch          ext  return  operands
---------------------------------------------------------------------------------
   6     0  >   ECHO                                                     'handler+called%0A'
         1      TICKS                                                    1
   7     2    > RETURN                                                   null

branch: #  0; line:     6-    7; sop:     0; eop:     2
path #1: 0, 
End of function handler.

**在php manual中，它说：

  

tick是由声明块内的解析器执行的每N个低级别可选语句发生的事件。在声明块的指令部分中使用ticks = N指定N的值。**

但是在示例脚本中，只要将ticks指定为1或2

，输出就相同