操作码EXT_STMT在Zend引擎中做了什么？

Question

似乎除了空文件之外的所有PHP文件都通过编译的操作码自由分散了操作码EXT_STMT。例如：

$ cat << EOF > hello.php
> <?php
> echo 'Hello';
> ?>
> EOF

$ php -dvld.active=1 -dvld.execute=0 hello.php
Finding entry points
Branch analysis from position: 0
Return found
filename:       /home/james/dev/php/hello.php
function name:  (null)
number of ops:  4
compiled vars:  none
line     # *  op                           fetch          ext  return  operands
---------------------------------------------------------------------------------
   2     0  >   EXT_STMT                                                 
         1      ECHO                                                     'Hello'
   4     2      EXT_STMT                                                 
         3    > RETURN                                                   1

branch: #  0; line:     2-    4; sop:     0; eop:     3
path #1: 0, 

这EXT_STMT做了什么？ Its entry in the manual几乎没有文档。