Physical Style Tags (HTML & XHTML: The Definitive Guide, 4th Edition)

4.5.1. The Tag

The  tag is the physical equivalent of the  content-based style tag, but without the latter's extended meaning. The  tag explicitly boldfaces a character or segment of text that is enclosed between it and its corresponding () end tag. If a boldface font is not available, the browser may use some other representation, such as reverse video or underlining.

4.5.2. The <big> Tag

The <big> tag makes it easy to increase the size of text. It couldn't be simpler: the browser renders the text between the <big> tag and its matching </big> ending tag one font size larger than the surrounding text. If that text is already at the largest size, <big> has no effect. Section 4.6.3, "The Tag (Deprecated)"

Even better, you can nest <big> tags to enlarge the text. Each <big> tag makes the text one size larger, up to a limit of size seven, as defined by the font model.

Be careful with your use of the <big> tag, though. Because browsers are quite forgiving and try hard to understand a tag, those that don't support <big> often interpret it to mean bold.

4.5.3. The <blink> Tag

Text contained between the <blink> tag and its end tag </blink> does just that: blink on and off. Netscape for Macintosh, for example, simply and reiteratively reverses the background and foreground colors for the <blink> enclosed text. Neither the HTML nor the XHTML standard include <blink>; it is supported as an extension only by Netscape Navigator.

We cannot effectively reproduce the animated effect in these static pages, but it is easy to imagine and best left to the imagination, too. That's because blinking text has two primary effects: it gets your reader's attention, and then promptly annoys them to no end. Blinking text should be used sparingly in any context.

Like <big>, you may also nest  tags to sequentially shrink text. Each  tag makes the text one size smaller than the containing  tag, down to a limit of size one.

4.5.7. The <strike> Tag (Deprecated)

Most browsers will put a line through ("strike through") text that appears inside the <strike> tag and its </strike> end tag. Presumably, it is an editing markup that tells the reader to ignore the text passage, reminiscent of the days before typewriter correction tape. You'll rarely, if ever, see the tag in use today, and probably never will: it is deprecated in HTML 4 and XHTML, just one version away from complete elimination from the standard.

4.5.8. The Tag

The text contained between the  tag and its  end tag gets displayed half a character's height lower, but in the same font and size as the current text flow. Both  and its  counterpart are useful for math equations and in scientific notation, as well as with chemical formulæ.

4.5.9. The Tag

The  tag and its  end tag superscripts the enclosed text; it gets displayed half a character's height higher, but in the same font and size as the current text flow. This tag is useful for adding footnotes to your documents, along with exponential values in equations. In combination with the <a> tag, you can create nice, hyperlinked footnotes:

The larval quat 
weevil<a href="footnotes.html#note74"><sup><small>74</small></sup></a> is a

This example assumes that footnotes.html contains all your footnotes, appropriately delimited as named document fragments.

4.5.10. The <tt> Tag

In a manner like the <code> and <kbd> tags, the <tt> tag and necessary </tt> end tag direct the browser to display the enclosed text in a monospaced typeface. For those browsers that already use a monospaced typeface, this tag may make no discernible change in the presentation of the text.

4.5.11. The Tag (Deprecated)

This tag tells the browser to underline the text contained between the  and the corresponding  tag. The underlining technique is simplistic, drawing the line under spaces and punctuation as well as the text. This tag is deprecated in HTML 4 and XHTML and will be eliminated in the next version of the standard. The same effect can be achieved by using style sheets, covered in Chapter 8, "Cascading Style Sheets".

4.5.12. The dir and lang Attributes

The dir attribute lets you advise the browser as to which direction the text within the physical tag ought to be displayed, and lang lets you specify the language used within the tag. Section 3.6.1.1, "The dir attribute" Section 3.6.1.2, "The lang attribute"

4.5.13. The class, id, style, and title Attributes

Although each physical tag has a defined style, you can override that style by defining your own look for each tag. This new look can be applied to the physical tags using either the style or class attributes. Section 8.1.1, "Inline Styles: The style Attribute" Section 8.3, "Style Classes"

You also may assign a unique id to the physical style tag, as well as a less rigorous title, using the respective attribute and accompanying quote-enclosed string value. Section 4.1.1.4, "The id attribute" Section 4.1.1.5, "The title attribute"

4.5.14. Event Attributes

Like with content-based style tags, user-initiated mouse and keyboard events can happen in and around a physical-style tag's contents. Many of these events are recognized by the browser if it conforms to current standards, and, with the respective "on" attribute and value, you may react to the event by displaying a user dialog box or activating some multimedia event. Section 12.3.3, "JavaScript Event Handlers"

4.5.15. Summary of Physical Style Tags

The various graphical browsers render text inside the physical style tags in similar fashion. Table 4-2 summarizes these browser's display styles for the native tags. Style sheet definitions may override these native display styles.

Table 4-2. Physical Style Tags

Tag	Meaning	Display Style
`<b>`	Bold contents	bold
`<big>`	Increased font size	bigger text
`<blink>`	Alternating fore- and background colors	blinking text
`<i>`	Italic contents	italic
`<small>`	Decreased font size	smaller text
`<s>`, `<strike>`	Strike-through text	~~strike~~
`<sub>`	Subscripted text	_subscript
`<sup>`	Superscripted text	^superscript
`<tt>`	Teletypewriter style	`monospaced`
`<u>`	Underlined contents	underlined

The following HTML source example illustrates some of the various physical tags as rendered by Netscape for Figure 4-12:

Explicitly <b>boldfaced</b>, <i>italicized</i>, or
<tt>teletype-style</tt> text should be used 
<big><big>sparingly</big></big>.
Otherwise, drink <strike>lots</strike> 1x10<sup>6</sup>
drops of H<sub><small><small>2</small></small></sub>O.