function parseDCC(source,start,domBuilder,errorHandler){//sure start with '<!'
	var next= source.charAt(start+2)
	switch(next){
	case '-':
		if(source.charAt(start + 3) === '-'){
			var end = source.indexOf('-->',start+4);
			//append comment source.substring(4,end)//<!--
			if(end>start){
				domBuilder.comment(source,start+4,end-start-4);
				return end+3;
			}else{
				errorHandler.error("Unclosed comment");
				return -1;
			}
		}else{
			//error
			return -1;
		}
	default:
		if(source.substr(start+3,6) == 'CDATA['){
			var end = source.indexOf(']]>',start+9);
			domBuilder.startCDATA();
			domBuilder.characters(source,start+9,end-start-9);
			domBuilder.endCDATA() 
			return end+3;
		}
		//<!DOCTYPE
		//startDTD(java.lang.String name, java.lang.String publicId, java.lang.String systemId) 
		var matchs = split(source,start);
		var len = matchs.length;
		if(len>1 && /!doctype/i.test(matchs[0][0])){
			var name = matchs[1][0];
			var pubid = false;
			var sysid = false;
			if(len>3){
				if(/^public$/i.test(matchs[2][0])){
					pubid = matchs[3][0];
					sysid = len>4 && matchs[4][0];
				}else if(/^system$/i.test(matchs[2][0])){
					sysid = matchs[3][0];
				}
			}
			var lastMatch = matchs[len-1]
			domBuilder.startDTD(name,pubid && pubid.replace(/^(['"])(.*?)\1$/,'$2'),
					sysid && sysid.replace(/^(['"])(.*?)\1$/,'$2'));
			domBuilder.endDTD();
			
			return lastMatch.index+lastMatch[0].length
		}
	}
	return -1;
}
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.