Parses the SSML (well-formedness, no DTD) and checks it against W3C SSML 1.1: <s...
https://ton.halowerk.com/v1/ssml-validateOverview
Parses the SSML (well-formedness, no DTD) and checks it against W3C SSML 1.1: <speak> with version="1.1", xml:lang and namespace; the content model of every element (e.g. no <p> in <s>, <desc> only in <audio>, lexicon/meta first); required attributes (say-as interpret-as, sub alias, phoneme ph, audio src, mark name, lexicon uri and xml:id); value syntax of break, emphasis, prosody and voice.