Cascading Style Sheets - HTML and XHTML: The Definitive Guide - page 535

The stress property controls the amount of inflection that is placed on
elements in the spoken text. Various languages have differing rules for
stressing syllables and adding inflection based on grammar and pro-
nunciation rules. The stress property accepts a value in the range of 0
to 100, with the default value of 50 corresponding to "normal" stress.
Using a value of 0 eliminates inflection in the spoken content. Values
over 50 increasingly exaggerate the inflection of certain spoken ele-
ments.
The richness property controls the quality or fullness of the voice. A
richer voice tends to fill a room and carries farther than a less rich, or
smoother, voice. Like pitch and stress , the richness property accepts
a numeric value in the range of 0 to 100, with a default value of 50.
Values approaching 0 make the voice softer. Values over 50 make the
voice fuller and more booming.
8.4.12.4. Pause properties
Like whitespace in a printed document, insert pauses in spoken content
to offset and thereby draw attention to content as well as to create a
better-paced, more understandable spoken presentation.
The pause-before and pause-after properties generate pauses just be-
fore or just after an element's spoken content. These properties accept
either an absolute time value (using the s or ms unit) or a percentage
value. With a percentage value, the pause is relative to the length of
time required to speak a single word. For example, if the speech rate
is 120 words per minute, one word, on average, is spoken every 0.5
seconds. A pause of 100 percent, therefore, would be 0.5 seconds long;
a 20 percent pause would be 0.1 seconds long, and so on.
The pause property sets both the pause-before and pause-after proper-
ties at once. Use one value for pause to set both properties; the first of
two values sets pause-before , and the second sets the pause-after prop-
erty value.