Character Formatting

If physical and logical styles produce the same result on the screen, why are there both?

In the ideal SGML universe, content is divorced from presentation. Thus SGML tags a level-one heading as a level-one heading, but does not specify that the level-one heading should be, for instance, 24-point bold Times centered. The advantage of this approach (it's similar in concept to style sheets in many word processors) is that if you decide to change level-one headings to be 20-point left-justified Helvetica, all you have to do is change the definition of the level-one heading in your Web browser. Indeed, many browsers today let you define how you want the various HTML tags rendered on-screen using what are called cascading style sheets, or CSS. CSS is more advanced thHTML, though, and will not be covered in this Tutorial.

Another advantage of logical tags is that they help enforce consistency in your documents. It's easier to tag something as <H1> than to remember that level-one headings are 24-point bold Times centered or whatever. For example, consider the <STRONG> tag. Most browsers render it in bold text. However, it is possible that a reader would prefer that these sections be displayed in red instead. (This is possible using a local cascading style sheet on the reader's own computer.) Logical styles offer this flexibility.

Of course, if you want something to be displayed in italics (for example) and do not want a browser's setting to display it differently, you should use physical styles. Physical styles, therefore, offer consistency in that something you tag a certain way will always be displayed that way for readers of your document.

Try to be consistent about which type of style you use. If you tag with physical styles, do so throughout a document. If you use logical styles, stick with them within a document. Keep in mind that future releases of HTML might not support certain logical styles, which could mean that browsers will not display your logical-style coding. (For example, the <DFN> tag -- short for "definition", and typically displayed in italics -- is not widely supported and will be ignored if the reader's browser does not understand it.)

Logical Styles

<DFN>

for a word being defined. Typically displayed in italics. (Chip-India the best giude to computing.)

<EM>

for emphasis. Typically displayed in italics. (Keep your Surroundings clean.)

<CITE>

for titles of books, films, etc. Typically displayed in italics. ( HTML for Beginners)

<CODE>

for computer code. Displayed in a fixed-width font. (The <stdio.h> header file)

<KBD>

for user keyboard entry. Typically displayed in plain fixed-width font. (Enter passwd to change your password.)

<SAMP>

for a sequence of literal characters. Displayed in a fixed-width font. (Segmentation fault: Core dumped.)

<STRONG>

for strong emphasis. Typically displayed in bold. (NOTE: Always check your links.)

<VAR>

for a variable, where you will replace the variable with specific information. Typically displayed in italics. (rm filename deletes the file.)

Physical Styles

<B>

bold text

<I>

italic text

<TT>

typewriter text, e.g. fixed-width font.