No bracket matching when using the proposed semantic tokens API in VSCode

I'm using the VSCode (Insider) Semantic Tokens API to provide XSLT 3.0/XPath 3.1 syntax-highlighting.

The goal is to avoid using a TextMate grammar as this is really too limited (VSCode Issues - 216) for syntax highlighting XSLT/XPath. There are performance issues with TextMate grammars also.

My implementation extends the Semantic Tokens sample and returns tokens with the 'operator' tokenType for characters {, (, [, ], ) and }.

I've modified settings.json as follows for the Extension Development Host but this makes no difference:

{
  "[typescript]": {},
  "git.enableSmartCommit": true,
  "git.autofetch": true,
  "[XPath]": {
    "editor.matchBrackets": "always"
  }
}

I hoped that bracket matching for these token types would be automatic, but this doesn't appear to be the case. Is there a workaround for this? Am I using the wrong tokenType? Should I put in a feature request?