我在一个源码程序中看到一些html文件。里面的代码如下：

#parse("_head.html")
   <script type="text/javascript" src="$webpath/library/js/area.js"></script>
#if($colse)
   <div class="error">$colse</div>
#else
    #if($paramerror)
        <div  id="toperrors" class="errors">$paramerror</div>
    #else
                <div class="register">
                    <form action="$webpath/register${exname}" method="post">
                       #if($isinvite)
                        <div>
                            <div class="l images"><a href="$spaceurl" title="$username"><img src="$userhead" /></a></div>
                            <div class="l">
                            <h3>注册您的$sitename帐户，并加为$username的好友</h3>
                            $invitecontent</div>
                        </div>
                        <div class="clearpix"></div>
                        #else
                            <h3>用户注册</h3>
                        #end

#end

#end

请问这是哪个方面的知识？我该去搜索怎样的资料才能了解这些知识？