This property refers to the median volume of the current voice. Pitch and inflection variations may vary well above and below this value. The default minimum and maximum values (0/100) should be controllable by the user.
<body style="volume: soft">
inherit: Explicitly sets the value of this property to that of the parent.
silent: No sound at all. The time time that would have been taken to aurally render the element is still taken, but no sound is made. Any specified ‘pause’ properties before/after the element are also rendered. This behavior is different than the ‘speak’ property being set to none.
x-soft, soft, medium, loud, x-loud: x-soft: Same as ’0′, soft: Same as ’25′, medium: Same as ’50′, loud: Same as ’75′, x-loud: Same as ’100′
[number]: A number between ’0′ and ’100′. ’0′ represents the minimum audible volume level (not the same effect as “silent”) and 100 corresponds to the maximum comfortable volume level.
[percentage]: This measure is relative to the inherited value for the Volume property, and is clipped to the range ’0′ to ’100′.