There are occasions where you might have a web page that displays a document that is subject to change and where you want to show on the web page itself when the content of the page is changed. This is the web page equivalent to crossing out the content to be deleted and writing in the additions on a paper version where you want people to be able to still see how the content looked before your changes. Word Processors also have a facility to mark the deleted and added text so that people can see both versions ot the document.
XHTML provides tags to mark the deleted and inserted sections as well be surrounding them in <del> </del> and <ins> </ins> tags respectively.
The default appearance of the content of these tags in most browsers will be to put a line through the centre of the content marked as deleted and to underline the inserted content Of course the exact representation doesn't matter since the names of these tags clearly identify what their intended use is.
This article written by Stephen Chapman, Felgall Pty Ltd.