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When analyzing annual crop yields, <dfn>rind spectroscopy</dfn> may prove useful. By
comparing the relative levels of saturated hydrocarbons in fruit from adjacent trees,
rind spectroscopy has been shown to be 87% effective in predicting an outbreak of
trunk dropsy in trees under four years old.
Notice that we delimit only the first occurrence of "rind spectroscopy"
with a <dfn> tag in the example. Good style tells us not to clutter the
text with highlighted text. As with the many other, content-related and
physical style tags, the fewer the better. [*] As a general style, especially
in technical documentation, set off new terms when they are first in-
troduced to help your readers better understand the topic at hand, but
resist tagging the terms thereafter.
[*] If you need convincing that less is better when applying the content-based and physical style tags,
try reading a college textbook in which someone has highlighted what he considered important words
and phrases with a yellow marker.
4.4.6. The <em> Tag
The <em> tag tells the client browser to present the enclosed text with
emphasis. For nearly all browsers, this means the text is rendered in it-
alic. For example, the popular browsers will emphasize by italicizing the
words always and never in the following HTML/XHTML source:
Kumquat growers must <em>always</em> refer to kumquats
as "the noble fruit," <em>never</em> as just a "fruit."
Adding emphasis to your text is tricky business. Too little, and the em-
phatic phrases may be lost. Too much, and you lose the urgency. Like
any seasoning, emphasis is best used sparingly.
Although invariably displayed in italic, the <em> tag has broader implica-
tions as well, and someday browsers may render emphasized text with
a different special effect. The <i> tag explicitly italicizes text; use it if
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