SUB是Subtraction的缩写， 你这里注释应该是减法吧。但是这里是不是特别用的呢？毕竟减法也是加法的一种

[chenyangguang]

//变量加法：
ASSIGN_SUB => ZEND_ASSIGN_SUB_SPEC_VAR_CONST_HANDLER,
ZEND_ASSIGN_SUB_SPEC_VAR_TMP_HANDLER,
ZEND_ASSIGN_SUB_SPEC_VAR_VAR_HANDLER,
ZEND_ASSIGN_SUB_SPEC_VAR_UNUSED_HANDLER,
ZEND_ASSIGN_SUB_SPEC_VAR_CV_HANDLER,
ZEND_ASSIGN_SUB_SPEC_UNUSED_CONST_HANDLER,
ZEND_ASSIGN_SUB_SPEC_UNUSED_TMP_HANDLER,
ZEND_ASSIGN_SUB_SPEC_UNUSED_VAR_HANDLER,
ZEND_ASSIGN_SUB_SPEC_UNUSED_UNUSED_HANDLER,
ZEND_ASSIGN_SUB_SPEC_UNUSED_CV_HANDLER,
ZEND_ASSIGN_SUB_SPEC_CV_CONST_HANDLER,
ZEND_ASSIGN_SUB_SPEC_CV_TMP_HANDLER,
ZEND_ASSIGN_SUB_SPEC_CV_VAR_HANDLER,
ZEND_ASSIGN_SUB_SPEC_CV_UNUSED_HANDLER,
ZEND_ASSIGN_SUB_SPEC_CV_CV_HANDLER,