说明：  主要系统简明地介绍了HTML_CSS_JAVASCRIPT语言的主要内容，让读者一目了然，对HTML_CSS_JAVASCRIPT有更直观系统地认识。
(Concise introduction to the major systems of the main content HTML_CSS_JAVASCRIPT language, allowing readers a glance, right HTML_CSS_JAVASCRIPT have a more intuitive understanding of the system.)