## Main()

1. <!DOCTYPE html> document type declaration
2. <Meta> Meta tags don’t do anything to the content that is presented in the browser window, but they are used by the likes of search engines to catalogue information about the web page.
Names: The most commonly used names are author, description, and keywords. Description is often used by search engines (such as Google) to display a description of a web page in its search results. Keywords used be important for SEO.
HTTP Equivalents:
3. Conditional Comments:<!--[if IE]>and<![endif]-->more in MS
4. tabindex for navigation with input and others
Page used focus with certain keys
5. Labels have the added bonus of visual browsers rendering the labels themselves clickable, putting the focus on the associated form field. Both name and id attributs are typically required; the name for the form to handle that field and the id for the label to associate it to. 这也解释了自定义一些自定义CSS的标签

6. fieldset and legend: 这个都没见过, 挺好看的 Link

7. select>optgroup>option 用的不多, optgroup用于分组
8. input[type="range"]经常见到过相关变形, 现在算是明白了.拖动栏
9. H5 特性标签 datalist 看了一下可以做索引, 这个可以用用看!