Top 100 Validation Errors To date, a total of 482,146 pages have been validated through W3CLove. Here is the list of the most common errors and warnings we've collected. Is your website valid? Top 100 errors list 1.required attribute "alt" not specified, 1,476,382 times. 2.& did not start a character reference. (& probably should have been escaped as &.), 803,325 times. 3.end tag for "img" omitted, but OMITTAG NO was specified, 691,666 times. 4.an attribute value specification must be an attribute value literal unless shorttag yes is specified, 526,452 times. 5.end tag for "br" omitted, but OMITTAG NO was specified, 523,679 times.