Resources > HTML and xHTML
This gives information about the HTML and xHTML hypertext markup languages.
Note : unless otherwise indicated, ‘HTML’ on this page denotes both HTML and xHTML.
HTML Specifications
HTML recommendations (i.e. specifications) are issued by the W3C (World-Wide Web Consortium). The specifications are:
- HTML 2.0: mainly of historical interest.
- HTML 3.2: roughly supported by IE3 and NN3; well supported by Opera 3.62.
- HTML 4.00: superceded by HTML 4.01.
- HTML 4.01: supported, poorly, by NN4; better by IE4; better still by IE5; well supported by IE6+, Mozilla 1.7+ (and its progeny - Camino, Firefox, SeaMonkey, etc.), NN7+, Safari, and Opera 7+.
- HTML 5: in the very early stages of being created, often silently updated. (A discussion of the HTML 4 and 5 differences is available.) Some new features — e.g. the <canvas> tag — are supported by Firefox, Opera, and Safari, but HTML 5 support will be uneven for a long time.
- xHTML 1.0: accepted by older browsers except NN1-NN3.
- xHTML 1.1: modularized xHTML 1.0 Strict, with poorer support by legacy browsers than xHTML 1.0. A related document is the W3C Note xHTML+SMIL Profile, integrating a SMIL 2.0 subset with xHTML, with modules for animation, content control, media objects, timing & synchronization, time manipulations, and transition effects.
- xHTML 2.0: draft of upcoming xHTML 2.0 standard.
Note : no browser completely and correctly implements any version of HTML; some modern browsers, however, come very close, e.g. Chrome, Firefox, IE7+, Mozilla, Opera, Safari, and SeaMonkey.
Note : some modern browsers implement the specifications more correctly if a DOCTYPE is specified in the HTML file [more...].
HTML Validators
Validators check to see whether HTML and xHTML files are syntactically correct, i.e. are written in accordance with the specifications.
Some validators are:
- Microsoft Office Validator: free.
- A Real Validator: software to validate files off-line, using Windows. Trialware. Recommended.
- W3C Validator: an on-line validation service. Free.
- WDG Validator: an on-line validation service. Free.
- WDG Off-line Validator: software to validate files off-line, using Unix. Free.
Note : links to various validators and code checkers can be found on the WDG and DMOZ sites.
Caution : some vendors sell code checkers but wrongly call them validators. [more...]
HTML Code Checkers
Code checkers (sometimes called syntax checkers or lint programs) check for problems in HTML code. Some checks are similar to those that validators do. Other checks are beyond the scope of validators, e.g. checking for missing files, missing anchor tags, missing end tags, broken links, browser compatibility problems, browser accessibility problems, etc.
Some HTML code checkers are:
- CSE’s HTML Validator.
Also a CSS code checker.
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A free ‘lite’ version is available. - LinkScan.
- Talicom’s HTML Power Tools. Not recently updated.
- W3C Link Checker: an on-line service to find broken links. Free.
- W3C mobileOK Checker: an on-line service to find possible problems in sites for mobile devices. Free.
- Weblight.
- Xenu’s Link Checker. Free.
Note : links to various validators and code checkers can be found on the WDG and DMOZ sites.
Caution : some vendors sell code checkers but wrongly call them validators. [more...]