Opcode Descriptions and Examples
PHP Manual

ASSIGN_DIM

PHP code

<?php
/*
 * 
 * opcode number: 147
 */
$b 1;
$a[1][2] = $b;
?>

PHP opcodes

Function name: (null)

Compiled variables: !0=$b, !1=$a

line#op fetchextreturn operands
60 ASSIGN     !0,1
71 FETCH_DIM_W   $1 !1,1
 2 ZEND_ASSIGN_DIM     $1,2
 3 ZEND_OP_DATA     !0,$3
84 RETURN     1

Opcode Descriptions and Examples
PHP Manual