HTML is often described as a system for formatting documents, and though in practice is fairly true, is not really what HTML was meant to be.
HTML was developed for the Web, with the idea that Web documents should be independent of particular platforms, i.e. different types of operating systems running on different types of computers.
To be able to do so, HTML was designed mainly as an information structuring system, that simply designates the relative flow of blocks of information in the document (major heading, secondary heading, normal paragraph, etc.), and leave it to the local browser (on a user’s machine) to decide how to represent that structure.
But even as browsers are programmed to be aware of HTML elements, different browsers may treat the same element differently; for instance, the type and sizes of fonts a particular browser uses to display headings and paragraphs.
The idea that Web authors should have more control over the desired appearance of content had long been proposed and consequently led to the adoption of formatting elements in later HTML specifications.
But while it does offer greater flexibility, in terms of setting an element’s display properties, it also proved to complicate the already existing incompatibilities between browsers, and made it much more difficult to maintain a large Web, where an author would have to reformat every element in every page, if a change in style was preferred.
W3C, the body that oversees the evolution of Web technology, has specified an alternative method for formatting hypertext documents: the use of Cascading Style Sheets (CSS).
Style sheets provide a more efficient means of setting element properties in a single file, which can be applied to all or selected pages in your Web.
The W3C advocates using HTML strictly for document structuring and CSS for general formatting, as they intend to phase out many of HTML’s presentation elements and attributes in the future.
A deprecated element or attribute is one that has been outdated by newer constructs. Deprecated elements are clearly indicated where appropriate, and authors should avoid their continued use, as they may gradually be phased out and become obsolete in future versions of HTML, as support for CSS matures.
The discussions of their function and use are necessary, however, to better understand their counterpart in the more recent CSS model.
Most of the attributes deprecated are, in general, those that have to do with HTML formatting. Authors are advised to use style sheets instead, to achieve the desired element rendering.
For reasons of backward compatibility, though, browsers shall continue to support deprecated elements until such time that CSS has become fully implemented.