JPM: How to personalize a toggle button tooltip label

Question

I have a toggle button in my addon. I want to personalize the CSS inside tooltip label who appear when you hover the button.

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Below example with Firebug icon tooltip label

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This is my toggle button

var button = ToggleButton({
  id: "S1",
  label: "Ultimate",
  icon: {
    "16": "./16-disabled.png",
    "32": "./32-disabled.png",
    "64": "./64-disabled.png"
  }
});

I have try a lot of solutions but never works.

label: "<strong>Ultimate</strong>" // Result: <strong>Ultimate</strong>
label: "<b>Ultimate</b>" // Result: <b>Ultimate</b>
label: "<div style='font-weight:bold'>Ultimate</div>" // Result: <div style='font-weight:bold'>Ultimate</div>

Just the \n\r work

label: "Ultim\nate" // Result: Ultim
                               ate