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Durham University

Computing and Information Services

Glossary of terms used

This glossary explains some of the terms used in the site.

Degrade Gracefully
An element of a web page is said to 'degrade gracefully' if ignoring it does not prevent information on the page from being displayed. For example, ignoring all HTML tags that denote emphasised text will 'degrade gracefully'. On the other hand, elements such as frames or Javascript navigation do not degrade gracefully by default and careful writing of code is needed to ensure that a lack of support does not make the site unusable.
Device Independence
The display of content, and any actions needed to interact with the content, should be device-independent. For example, the scripting events onclick and onkeypress are device-dependent: they can only be used by a mouse or keyboard respectively. However, the scripting events onfocus and onchange are device-independent, as it does not matter how the element is focused on or changed.
Content is said to linearise if it can still be sensibly read despite any code that determines its layout and position being removed. The two major areas where linearisation must be considered are:
  • Display without stylesheets
  • Display without support for tables
Presentational Markup
Presentational Markup is HTML used to control the appearance of a page. For example, the <tt> tag makes text appear in a monospaced font. Presentational markup is meaningless outside of a visual medium - in this case, one of the <code>, <samp>, or <kbd> elements might be more useful. The use of presentation markup is strongly discouraged in most circumstances. Bold and italic markup are generally best replaced by emphasis markup, except for circumstances where the convention is for bold or italic text without any particular logical emphasis (e.g. scientific names, or parts of citations)
Structural Markup
Structural Markup is used to set out the logical structure of a page. The <strong> tag (Text style strong in Dreamweaver) identifies that text as strongly emphasised. In most visual media, this will normally be displayed as bold text, but in non-visual media, the emphasis can be retained. Structural markup makes the structure of the document clearer both to browsers (which can then display it more usefully to their users), and to search engines. The use of structural markup is strongly recommended.
Style Sheets
When using Structural Markup, there is no way to suggest presentation in the HTML code itself. Instead, Cascading Style Sheets are used to suggest the presentation of structural markup in various display media.
Text Equivalent
A Text Equivalent to an element is text to be displayed when the element is either not displayed or cannot be displayed (they may be displayed when the original element is displayed, but this should not be relied on). A text equivalent should fulfil the same purpose as the original element. For example, the text equivalent of a picture of text would be the text itself. If the image is a photograph of some text, consider the purpose of the image and make the text equivalent accordingly. Methods of specifying text equivalents vary from element to element. A useful technique for determining the appropriate text equivalent is to consider what text you would put there if you were unable to use the type of non-text content that you have.