This is relevant to HTML validation. For XHTML and most other document formats it is irrelevant, as XHTML fixes the HTML quirks it deals with. XHTML is automatically detected, and you can safely ignore this option when validating XHTML and XML documents.
Strictly speaking, this is the only mode that offers true HTML validation. However, this allows various constructs that will break in most mainstream browsers, and should be used with caution.
For example, the following is a valid HTML document:
<!DOCTYPE HTML PUBLIC "-//W3C//DTD HTML 4.01//EN"> <title/HTML example/ <p<p/This is the second paragraph in this document. The first was empty.
Note the missing
>s - this will confuse browsers!
Web Mode will generate additional warnings about these quirks. This is strongly recommended for HTML documents. It is somewhat similar to the "warnings" option of the WDG Validator.
Fussy mode adds further checks over and above Web Mode. These are, in our view, seldom necessary, but may be considered Good Practice. The main effect is to cause the validator to insist on tags that are implied by your markup being made explicit. This mode is most useful with the Visual Validator view, as the Normalised Source display will help you by including the implicit tags it is asking for.