Sometimes you might want to configure how a voice sounds, for example the speed, prosody or other ways. These alterations are voice-provider specific, i.e Cereproc has their own tags and Acapela has their own tags.
Cereproc voice tags
Please see the Cereproc Tagset document
Acapela voice tags
Please see section 4 ("Text tags") in Acapela Usermanual document