A comment by Paperhead in the Signal Vs. Noise blog mentioned a link to a W3School article commenting on CSS2 and the aural properties in stylesheets.
The link to the article reference page is here: www.w3schools.com/css/css_ref_aural.asp and the W3C Aural Stylesheet pages are here
www.w3.org/TR/REC-CSS2/aural.html
Some of the properties of CSS2 allows the ability to control volume, pause, cue, spacial, speech rate, pitch, pronunciation and richness.