Tham khảo tài liệu 'tự học html và css trong 1 giờ - part 57', công nghệ thông tin, đồ họa - thiết kế - flash phục vụ nhu cầu học tập, nghiên cứu và làm việc hiệu quả | 536 lesson 18 Writing Good Web Pages Do s and Don ts FIGURE The W3 Validator. If you look closely at the screenshot you can see that at the time I validated this page it came out with 42 errors all of which are violations of the XHTML Transitional recommendation. The page looks fine in the popular browsers but it s not in sync with the recommendation. The errors generally fall into two categories missing closing tags usually for the img tag and missing required attributes mainly the alt attribute for img tags . This page also includes some invalid attributes for tags. One common error that appears on this page refers to an entity with no system identifier and a longer set of errors related to the same bit of markup. The problem here is that the validator expects the character to be the beginning of an entity but on this page it is part of the URL for a link. To avoid these errors the ampersands in links need to be encoded as amp . You can see this entity-related error in Figure . Download from Standards Compliance and Web Browsers 537 FIGURE Error messages produced by the W3 Validator. In the screenshot you ll see that each error is accompanied by the subset of the page s source where the error appears along with an explanation for the error. After you ve fixed all the errors on your page you ll be privileged enough to see the message indicating that your page is valid as shown in Figure . FIGURE The W3 Validator acknowledges a job well done. Download from 538 lesson 18 Writing Good Web Pages Do s and Don ts HTML Tidy If you have some existing pages and you re not up for the challenge of turning them into valid HTML there s a program that will not only validate your pages but also correct them as best as it can. This program HTML Tidy was originally written by a staffer at the W3C named David Raggett and has since been handed over to the community for maintenance. You can obtain it at http .
