What is your opinon about following regexes - is it correct? To find element with spcific and required attribute "<(" + elem_name + ")(\s+(?:[^<]?\s+)" + attr_name + "\s*=\s*(['\"])((?:(?!\3).))\3[^<])(.*?)" To find element with spcific but optional attribute "<(" + elem_name + ")(\s*|\s+(?:[^<]?\s+)(?:" + attr_name + "\s*=\s*(['\"])((?:(?!\3).))\3)?[^<])(.*?)" Pleas not another answer "use existing xml parser". Question is - are the regexes proper or not? This is specific situation - C language in embedded system and xml is not well-formed (cannot be fixed - does not depend on me). Xml have specified schema and no problem with namespaces etc. exists.