A full list of options can be found here.

time Sets the length of the break by seconds or milliseconds (e.g. "3s" or "250ms").

strength Sets the strength of the output's prosodic break by relative terms. Valid values are: "x-weak", weak", "medium", "strong", and "x-strong". The value "none" indicates that no prosodic break boundary should be outputted, which can be used to prevent a prosodic break that the processor would otherwise produce. The other values indicate monotonically non-decreasing (conceptually increasing) break strength between tokens. The stronger boundaries are typically accompanied by pauses.

level Could be "strong", "moderate", "none" or "reduced".

Example <emphasis level="moderate">This is an important announcement</emphasis>

interpret-as "cardinal" would say 'Twelve thousand and fifty' if you wrote <say-as interpret-as="cardinal">12050</say-as>

interpret-as "ordinal" would say 'First' if you wrote <say-as interpret-as="ordinal">1</say-as>

interpret-as "characters" would say 'C A N' if you wrote <say-as interpret-as="characters">can</say-as>

interpret-as "fraction" would say 'Five an a half' if you wrote <say-as interpret-as="fraction">5+1/2</say-as>

Example <p><s>This is sentence one.</s><s>This is sentence two.</s></p>

Best practice Use <s>...</s> tags to wrap full sentences, especially if they contain SSML elements that change prosody (that is, <audio>, <break>, <emphasis>, <par>, <prosody>, <say-as>, <seq>, and <sub>). If a break in speech is intended to be long enough that you can hear it, use <s>...</s> tags and put that break between sentences.