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HomeWeb Front-endHTML Tutorial与html相关的知识点整理_html/css_WEB-ITnose

梳理html时发现的一些问题。总结一下,答案大都从网上找来。

一.html 与 htm 的区别

没有本质的区别。.htm是在win32时代,系统只能识别3位扩展名时使用的。现在一般都使用.html。

 

二.href 与 src 的区别

src是source的缩写,指向外部资源的位置,指向的内容将会嵌入到文档中当前标签所在位置;在请求src资源时会将其指向的资源下载并应用到文档内,例如js脚本,img图片和frame等元素。

 

<script src ="js.js"></script>

 

当浏览器解析到该元素时,会暂停其他资源的下载和处理,直到将该资源加载、编译、执行完毕,图片和框架等元素也如此,类似于将所指向资源嵌入当前标签内。这也是为什么将js脚本放在底部而不是头部。

 

href是Hypertext Reference的缩写,指向网络资源所在位置,建立和当前元素(锚点)或当前文档(链接)之间的链接,如果我们在文档中添加

 

<link href="common.css" rel="stylesheet"/>

 

那么浏览器会识别该文档为css文件,就会并行下载资源并且不会停止对当前文档的处理。

 

三. 引入层叠样式表时 使用link 和 使用@import 的区别

1.老祖宗的差别。link属于XHTML标签,而@import完全是CSS提供的一种方式。

link标签除了可以加载CSS外,还可以做很多其它的事情,比如定义RSS,定义rel连接属性等,@import就只能加载CSS了。

2.加载顺序的差别。当一个页面被加载的时候(就是被浏览者浏览的时候),link引用的CSS会同时 被加载,而@import引用的CSS 会等到页面全部被下载完再被加载。所以有时候浏览@import加载CSS的页面时开始会没有样式(就是闪烁),网速慢的时候还挺明显(梦之都加载CSS 的方式就是使用@import,我一边下载一边浏览梦之都网页时,就会出现上述问题)。

3.兼容性的差别。由于@import是CSS2.1提出的所以老的浏览器不支持,@import只有在IE5以上的才能识别,而link标签无此问题。

4.使用dom控制样式时的差别。当使用javascript控制dom去改变样式的时候,只能使用link标签,因为@import不是dom可以控制的。

 

四.i/em 与 b/strong 的区别

在HTML4.01中: 是 视觉要素(presentationl elements),分别表示无意义的加粗,无意义的斜体,表现样式为 { font-weight: bolder },仅仅表示「这里应该用粗体显示」或者「这里应该用斜体显示」,此两个标签在HTML4.01中并不被推荐使用;
和 是 表达要素(phrase elements)。 (emphasized text)表示一般的强调文本,而 (strong emphasized text)表示比 语义更强的的强调文本。

而在新的 HTML5 工作草案 中: 和 仍旧是表达要素(phrase elements)。但这时的 表示html页面上的强调(emphasized text), 表示句子中的强调(即强调语义)

 

 

五.域名 与 网站名 的区别

域名之与网站名相当于土地之与土地上的建筑,在这块土地上你可以建造任意数量的建筑。

baidu.com    //域名

http://news.baidu.com/      //网站名 由服务器名+域名组成;http为传输协议

http://map.baidu.com/          百度地图

 

六. meta 标签的作用

元素可提供有关页面的元信息(meta-information),比如针对搜索引擎和更新频度的描述和关键词。

标签位于文档的头部,不包含任何内容。 标签的属性定义了与文档相关联的名称/值对。

详细:http://www.w3school.com.cn/tags/tag_meta.asp

 

 

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