Use the break tag for pacing long sentences instead of padding with punctuation, and the sub tag for brand names and acronyms the default voice mangles. Only these two tags are documented - other SSML tags are not supported, so do not assume full SSML works.

Context: Synthesia API scripts support a small set of XML-like tags for timing and pronunciation (official docs: Script supported XML tags). The break tag inserts a pause: Hello [break time="2s"/] world. The time attribute takes seconds and it works with all voices. The sub tag controls pronunciation: the alias attribute is what the avatar says, the inner text is what appears in captions. Example: The word is [sub alias="Syn-the-zia"]Synthesia[/sub] - the avatar says 'Syn-the-zia' while captions show 'Synthesia'.