Comment: The syntax changes of HTML5 are mainly reflected in the fact that tags are no longer case sensitive, elements can omit end tags, attributes that allow attribute values to be omitted, etc. Interested friends can refer to it, hoping that it will be helpful for everyone to understand HTML5.
1. Labels are no longer case sensitive<p>Hello,World!</P>
2. Elements can omit the end tag
(1) Elements of empty element syntax: area, base, br, col, command, embed, hr, img, input, keygen, link, mata, param, source, wbr
(2) Elements that end tags can be omitted: colgroup, dt, dd, li, optgroup, p, rt, rp, thread, tbody, tfoot, tr, td, th
(3) All elements that can be omitted: html, head, body, tbody
3. Allow attributes that omit attribute values
4. Allow attribute values to be without quotes