set data(data){
        // throw Exception if Node is readonly
        if (__ownerDocument__(this).errorChecking && this._readonly) {
            throw(new DOMException(DOMException.NO_MODIFICATION_ALLOWED_ERR));
        }
        this.nodeValue = data;
    }
@class  ProcessingInstruction -
     The ProcessingInstruction interface represents a
     "processing instruction", used in XML as a way to
     keep processor-specific information in the text of
     the document
@extends Node
@author Jon van Noort (jon@webarcana.com.au)
@param  ownerDocument :  The Document object associated with this node.