The following HTML4 elements have been removed from HTML5.
1. Mixing of uppercase and lowercase for element name is bad, lower is recommended
2. Close All HTML Elements
3. Close All Empty HTML Elements
4. Use Lower Case Attribute Names
5. Spaces around equal signs is legal, But space-less is easier to read
6. Make the title as meaningful as possible
7. To ensure proper interpretation, and correct search engine indexing, both the language and the character encoding should be defined as early as possible in a document
<title>HTML5 Syntax and Coding Style </title>
8. Place the opening bracket on the same line as the selector.
9. Use one space before the opening bracket.
10. Use 2 spaces of indentation.
11. Use colon plus one space between each property and its value.
12. Use space after each comma or semicolon.
13. Use semicolon after each property-value pair, including the last.
14. Only use quotes around values if the value contains spaces.
15. Place the closing bracket on a new line, without leading spaces.
16. Use Lower Case File Names
17. There is no difference between the .htm and .html extensions.
18. When a URL does not specify a filename (like http://www.ankitweblogic.com/html5/), the server returns a default filename like index.html, index.htm, default.html, and default.htm.
19. If your server is configured only with "index.html" as default filename, your file must be named "index.html", not "index.htm."