Pop one string or an integer (member name), pop an object reference, define the value of that object member and push the result back on the stack.
Objects include some special members such as:
|_parent||Retrieve the parent object of this object.|
Note that in ActionScript these special members are not written with the underscore character. (i.e. you may find this.parent in a script, and parent will be converted to _parent the SWF movie.)