I think this change should probably only be made to ActionableNotification.

InlineNotification and ToastNotification can only have a role of alert, status, or log, which means:

• All semantic value (rich text, line breaks, etc) placed in the subtitle would not be read by screenreaders.
• These components can't contain interactive elements like hyperlinks

For those reasons I think it makes the most sense to keep subtitle as a plain string in InlineNotification and ToastNotification.

Opening up subtitle to be a node in ActionableNotification should be fine though because it gets a role of alertdialog, which preserves semantic value and can include interactive elements.

@crhuff-ibm Sorry for the delayed response here. If you're using any rich text decoration you'll need to use ActionableNotification.

I've updated the PR so that ActionableNotification's actionButtonLabel is now optional and the button isn't rendered if the actionButtonLabel isn't provided. This makes it so you can configure just subtitle without an action.

With this PR, your usage would look something like this:

export default function App() {
  const subtitle = (
    <span>
      I've got some <strong>rich</strong> <em>text</em>{' '}
      <strong>
        <em>here</em>
      </strong>
    </span>
  );
  return (
    <div>
      <ActionableNotification inline subtitle={subtitle} />
    </div>
  );
}

Ideal tradeoff 👍🏻
LGTM 👍 ✅