How do Azure AI Speech and Google Cloud Text-to-Speech document emphasis, prosody and style control, and what are the caveats for HD or newer voices?

Problem: choose markup that the target voice honours. Conditions: Azure Speech SSML and Google Cloud TTS SSML as documented. Method (Azure): <prosody> adjusts pitch, contour, range, rate and volume (contour takes percent/pitch pairs); <emphasis> word-level stress tuning is documented only for en-US-GuyNeural, en-US-DavisNeural and en-US-JaneNeural, and the page warns low-pitch, short words may not be raised enough to notice. For HD voices (DragonHD family) expressive control moves to styles: <mstts:express-as style=...> or inline style markers such as [whispering]; a marker applies to all later sentences until reset with [Neutral], and \r\n, <p> and automatic sentence boundaries reset to default style while <break> does not. Style degree 0.01-2 is ignored if unsupported for the voice. (Google): the page states that not all elements of the W3C spec are supported; <emphasis> levels are strong, moderate, none, reduced; it advises using <emphasis> and <prosody> only around full sentences because wrapping words inside a sentence may cause unwanted pauses, and wrapping sentences in <s> when markup changes prosody. Use (inference): keep a per-voice capability table in the pipeline; for style-capable voices use style tags, for others use sentence-level prosody; always audition. Failure modes: word-level emphasis on unsupported voices does nothing; unreset style markers leak into later lines. Limitations: pages undated; HD voice lists and styles change often; I did not synthesise audio. Curator qualifications: All cited documentation excerpts located on the live pages by curator GET; no video sources. Limitations: Vendor lists are moving targets; no listening test performed. Which Google voice families (e.g. newer HD/Chirp) accept which tags is not covered by the text I read. Evidence status: statements located in the cited sources by a correlated desk review (Claude); not executed; not independently reviewed.

{
  "citations": [
    {
      "url": "https://learn.microsoft.com/en-us/azure/ai-services/speech-service/speech-synthesis-markup-voice",
      "note": "Adjust emphasis; Styles and paralinguistic in HD voices; Styles and paralinguistic in HD voices; Support for SSML elements; emphasis"
    },
    {
      "url": "https://cloud.google.com/text-to-speech/docs/ssml",
      "note": "Adjust emphasis; Styles and paralinguistic in HD voices; Styles and paralinguistic in HD voices; Support for SSML elements; emphasis"
    }
  ]
}