HTML modes

About HTML

Most of the documents ("pages") found on the World Wide Web are written in HTML (HyperText Markup Language). HTML was originally designed as a standard hard- and software independent way of formatting documents. It is an application of SGML (Standard Generalized Markup Language).

The only official standard is HTML 2.0, which contains very limited possibilities. The W3 consortium was developing a new, extended standard, HTML 3.0.

Meanwhile, in the recent boom of Internet and the World Wide Web, some browser manufacturers have introduced several ad-hoc extensions to HTML, of which many didn't fit in the new HTML 3.0 standard. Probably because this would make HTML 3.0 an academic standard without any practical use, the development of HTML 3.0 was abandoned. AWeb supports some of the extensions found in HTML 3.0.

In the first half of 1996 the W3 group proposed a new HTML 3.2 standard, which contains many of the widely used NetScape ® and Microsoft ® Internet Explorer specific extensions. In 1997 its successor, HTML 4.0 is proposed. AWeb fully supports HTML 3.2 and many features of HTML 4.0 (one major exception being style sheets).

The large browser manufacturers have introduced other tags, that aren't included in the HTML standard. AWeb will try to support most of these non-standard extensions.

To make things even more inconvenient, some earlier versions of popular PC browsers didn't stick to the SGML rules. And even recent versions of those browsers still have problems with SGML comments. Because many people design their pages using these browsers, there are many documents on the web that just are bad HTML.

HTML modes

AWeb does its best to display all pages correctly, but sometimes you have to set the way HTML should be interpreted to get the best results.

You can choose out of three HTML modes:

Strict In strict HTML mode, AWeb understands only the HTML standard.
Tolerant In tolerant HTML mode, AWeb understands also other extensions. These are both extensions specific to other browsers, and HTML 3.0 extensions that can't be found in HTML 3.2 or HTML 4.0.
Also, some commonly made errors are correctly understood. See below for a list of corrected errors.
Compatible In compatible HTML mode (a nice way of formulating "buggy"), AWeb tries to interpret buggy HTML. Below is a description of the deviations of the standard when compatibility mode is used.
Set one of these in the Options page in the browser settings.

Strict	In strict HTML mode, AWeb understands only the HTML standard.
Tolerant	In tolerant HTML mode, AWeb understands also other extensions. These are both extensions specific to other browsers, and HTML 3.0 extensions that can't be found in HTML 3.2 or HTML 4.0. Also, some commonly made errors are correctly understood. See below for a list of corrected errors.
Compatible	In compatible HTML mode (a nice way of formulating "buggy"), AWeb tries to interpret buggy HTML. Below is a description of the deviations of the standard when compatibility mode is used.

The overview of supported HTML mentions with each HTML tag or attribute in which mode it is recognized.

Tolerant mode

In tolerant mode, AWeb recovers from the following commonly made HTML errors:

Incorrectly placed tags in <TABLE>, like missing <TD>, or <FORM> between <TABLE> and the first <TR>.
Invalid "&#nnn;" entities, that contain a number that is not included in the HTML Coded Character set, are converted to whitespace.
Many forms of incorrect comments. When AWeb encounters a comment, it starts by assuming the comment is correct, but if it encounters something that does not belong in a correct comment, it terminates the comment at the first ">". This catches most of the incorrect comment usage, but it is still possible that some of the HTML is inadvertently commented out.
When an URL in a hyperlink contains whitespace (a common source of this whitespace is the HREF or SRC attribute being broken over two lines), this whitespace is removed.
If a resulting absolute URL contains a path beginning with one or more "../", these are removed.

Compatible mode

As mentioned above, some pages contain bad HTML. When you view such a page, it can look distorted. You can expect large parts of the page missing, links to URLs that seem to contain HTML tags, and other strange things.

If you encounter such problems, try using the compatible HTML mode of AWeb. Warning: Using compatible HTML mode, documents containing valid HTML might look distorted in turn.

In compatible mode, AWeb exposes the following deviations from the SGML and HTTP standards:

Quoted attribute values are terminated by any occurrence of ">"
Quoted attributes that contain URLs, like HREF, SRC and ACTION, are terminated by whitespace
Comments are terminated by any occurrence of "->"
When a server responds to a POST request with a HTTP redirection (status 301 or 302), the new location is accessed with the GET method instead of POST.

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