The information here is mildly technical in nature, but should be understood if read carefully.
The technologies discussed here form a subset of those available on the web and with which Ascent Software can undertake development.
Most web-pages on the internet are written in what is called HTML, which stands for hyper-text markup language. There are several versions of HTML around, most recent is HTML 4.01 and XHTML 1.0. The 'X' in XHTML stands for 'eXtensible'. XHTML provides web authors with far more content and presentation control than HTML, capable of working on a far wider range of devices. The W3C website provides a full statement of current research and future direction of XHTML.
So, most web documents will be HTML or XHTML based. Because some users on the web use older browser programs (which only know about previous versions of HTML), some web-pages use deprecated features to control presentation. To cater for this, a 'loose' standard exists which allows out of date techniques to work on modern browsers. A web-document of this type is said to be of 'Document Type Definition - Transitional'. The W3C provide a specification for Transitional HTML4.01. If you are interested in finding out what is now deprecated or obsolete, again the W3C site has the information.
Sadly, many web-authors are reliant upon deprecated features and are selling web-pages which will not be accessible and risk becoming nothing but a frustration for visitors in the future. Deprecated features can be safely ignored, but they tend to damage accessibility. Hence the W3C recommend compliance with the 'strict' model (see below).
You may wish to study the various HTML document type definitions (DTDs) yourself.
Web pages complying with the Transitional DTD can display this icon:
Web pages complying with Strict DTD must not use obsolete or deprecated HTML and as such are more amenable to running on a wide range of systems, some of which do not even exist yet. Such pages can display the same icon as for transitional HTML
A page complying with the XHTML DTD can display this icon: (this page does not comply).
XHTML is the next stage in web document technology.
There are several other DTDs which you can find on the W3C site.
Ascent Software's existing websites typically comply with HTML transitional or HTML strict. Future websites will be XHTML compliant.
A web-site may be presented visually or perhaps aurally, through text-to-speech technology. To assist with presenting a page in an attractive, yet accessible manner, Ascent Software uses Cascading Style Sheets (CSS). This technology permits a seperation of the content of a document from the presentation - essential in the multifarious internet. Central to the rationale of stylesheets is 'Useable Failure'. Older browsers which do not know about modern techniques, will still give a serviceable page, even if presentation goes wrong a bit (which, ideally, the user will not even be aware of). In the worst case, the user can switch off style sheets. (Netscape 4 for example, had particularly poor style sheet support).
As for HTML, standards have been written for CSS. There are two levels in common use, logically called CSS1 and CSS2 (the most recent).
Ascent Software uses CSS2 on our websites. Pages using CSS which complies to the specifications of the W3C can display this icon:
At present the majority of web users access pages using Microsoft's Internet Explorer, using a IBM compatible PC. But not all! Many users use Apple Macs, many more use Sun workstations (e.g. Sun Ultra), some will use handhelds from Palm, Handspring, Psion, HP, Casio or Compaq. These computers use an equally varied range of operating systems - perhaps Windows98, 2000 or NT, Linux (with countless variants), Unix, BeOS, EPOC, Chorus, MacOS, OS/2, Palm OS, Symbian, Windows CE ... get the picture? These are called platforms and there are plenty of them.
Well, we are not finished yet! A user has a further choice of browser. Again, there are many to choose from, most with several versions - including, Internet Explorer, Netscape, Lynx, Opera, IBM's 'Home Page Reader', WebSound or others.
So, in order to increase the chances that your site can be accessed from a wide range of platforms and browsers, the answer is to insist on standards compliance and on accessibility.
Support for old browsers? Ascent subscribes to the spirit of the Browser Upgrade Campaign. Users with out of date browsers should disable style sheets if they experience problems. (Upgrading their browser is a preferable option!)
An ISO standard exists for internet documents. The actual ISO standard itself is very terse and in practice a user's guide to ISO/IEC 15445:2000 is easier to read. Ascent does not claim to comply to the ISO standard, however we do use the standard for guidance on improving accessibility.
Accessibility refers to the the degree to which a web-site or web-document is usable by any person with a disability. For example, a person accessing your site may be have a visual impairment or motor difficulty. Improving accessibility is an honourable goal, in line with the spirit of the web. Quoting from the W3C: The power of the Web is in its universality. Access by everyone regardless of disability is an essential aspect.
The Disability Discrimination Act (1995) ... For other worldwide policies try W3C Accessibility Policies - Link Page"
The degree to which a website is accessible is tricky to ascertain precisely. However the W3C provides three levels of priorities for web authors to assess their work:
The above is from the W3C web accessibility initiative website.
In addition, there are many other third parties offering web accessibility checking and advice. For example, the 'Bobby' website has a facility which will assess the accessibility of a website automatically. Visit the Bobby accessibility website. Automated accessibility tools are limited in their efficacy - the only way to be sure of accessibility is to try it out!
All material © Ascent Software Ltd.
