HTML? XHTML? Standards and compatibility
Pass the 10 most popular sites to http://validator.w3.org/ and see the results: Page Document type HTTP Content-Type Errors Warnings Google HTML 5 text/html 48 2 Facebook XHTML 1.0 Strict text/html 39 0 YouTube HTML 4.01 Transitional text/html 154 52 Yahoo! HTML 4.01…