The right way to use SSML with Web Speech API

There are bugs for this issue currently open with Chromium.

• 88072: Extension TTS API platform implementations need to support SSML
• 428902: speechSynthesis.speak() doesn't strip unrecognized tags This bug has been fixed in Chrome as of Sept 2016.

I've tried this using Chrome 104.0.5112.101 (on Linux). Didn't work. When checking the debugging console I got the message:

speechSynthesis.speak() without user activation is deprecated and will be removed

Adding a button like mentioned in The question of whether speechSynthesis is allowed to run without user interaction does work for me. At least to speak out text, not SSML formatted text though.

In Chrome 46, the XML is being interpreted properly as an XML document, on Windows, when the language is set to en; however, I see no evidence that the tags are actually doing anything. I heard no difference between the <emphasis> and non-<emphasis> versions of this SSML:

var msg = new SpeechSynthesisUtterance();
msg.text = '<?xml version="1.0"?>\r\n<speak version="1.0" xmlns="http://www.w3.org/2001/10/synthesis" xml:lang="en-US"><emphasis>Welcome</emphasis> to the Bird Seed Emporium.  Welcome to the Bird Seed Emporium.</speak>';
msg.lang = 'en';
speechSynthesis.speak(msg);

The <phoneme> tag was also completely ignored, which made my attempt to speak IPA fail.

var msg = new SpeechSynthesisUtterance();
msg.text='<?xml version="1.0" encoding="ISO-8859-1"?> <speak version="1.0" xmlns="http://www.w3.org/2001/10/synthesis" xmlns:xsi="http://www.w3.org/2001/XMLSchema-instance" xsi:schemaLocation="http://www.w3.org/2001/10/synthesis http://www.w3.org/TR/speech-synthesis/synthesis.xsd" xml:lang="en-US"> Pavlova is a meringue-based dessert named after the Russian ballerina Anna Pavlova. It is a meringue cake with a crisp crust and soft, light inside, usually topped with fruit and, optionally, whipped cream.  The name is pronounced <phoneme alphabet="ipa" ph="p&aelig;v&#712;lo&#650;v&#601;">...</phoneme> or <phoneme alphabet="ipa" ph="p&#593;&#720;v&#712;lo&#650;v&#601;">...</phoneme>, unlike the name of the dancer, which was <phoneme alphabet="ipa" ph="&#712;p&#593;&#720;vl&#601;v&#601;">...</phoneme> </speak>';
msg.lang = 'en';
speechSynthesis.speak(msg);

This is despite the fact that the Microsoft speech API does handle SSML correctly. Here is a C# snippet, suitable for use in LinqPad:

var str = "Pavlova is a meringue-based dessert named after the Russian ballerina Anna Pavlova. It is a meringue cake with a crisp crust and soft, light inside, usually topped with fruit and, optionally, whipped cream.  The name is pronounced /pævˈloʊvə/ or /pɑːvˈloʊvə/, unlike the name of the dancer, which was /ˈpɑːvləvə/.";
var regex = new Regex("/([^/]+)/");
if (regex.IsMatch(str))
{
    str = regex.Replace(str, "<phoneme alphabet=\"ipa\" ph=\"$1\">word</phoneme>");
    str.Dump();
}   
SpeechSynthesizer synth = new SpeechSynthesizer();
PromptBuilder pb = new PromptBuilder();
pb.AppendSsmlMarkup(str);
synth.Speak(pb);