Some browsers are more forgiving of incorrect code than others, but just because something displays correctly on your screen, it doesn't mean other people will see the same thing. You should check your site on as many different machines and browsers as possible. If you use your own designs (as opposed to one of the University designs) you should test your pages very thoroughly. If you are using one of the University designs, at the very least you should test on both Internet Explorer and Firefox, with images on and off, and with and without stylesheets (if you use them).
Validating your HTML code so that it is free of errors will increase the chance of your site displaying well on a range of browsers. Making a mistake in the code syntax can result in problems. Some authoring tools also create invalid code that should be corrected.
For information on accessibility, see the internal page Web Accessibility Service.
HTML 4.01 is the last "HTML" standard. XHTML 1.0 is the current standard.
Times Higher Education, Student Experience Survey 2010-2015