	addValue:function(qName, value, offset) {
		if(!tagNamePattern.test(qName)){
			throw new Error('invalid attribute:'+qName)
		}
		this.attributeNames[qName] = this.length;
		this[this.length++] = {qName:qName,value:value,offset:offset}
	},
Product A handles inputs or steps differently than Product B, which causes A to perform incorrect actions based on its perception of B's state.