Docs for "automatic" tags

[mmkal]

I'd like to parse the browser tag that is automatically added by who knows which integration:

The only docs I can find for these tags are:

Some tags are automatically set by Sentry. We strongly recommend against overwriting those tags. Instead, name your tags with your organization's nomenclature.

Which isn't all that helpful since the automatically-set tags aren't listed anywhere! I've tried adding a beforeSend with something like:

  beforeSend: (event, hint) => {
    event.tags ||= {}

    const browserInfo = typeof event.tags?.browser === 'string' ? parseBrowserInfo(event.tags.browser) : null
    if (browserInfo?.type) {
      event.tags.browser_type ||= browserInfo.type
    }
    if (browserInfo?.version) {
      event.tags.browser_version ||= browserInfo.version?.string
    }
    if (browserInfo?.usageUpperBound) {
      event.tags.browser_usage_estimate ||= browserInfo.usageUpperBound?.usagePercent
    }

    return event
  },

But event.tags.browser is always undefined - the browser tag somehow appears magically on the Sentry app without having been in the original event or hint that was passed to beforeSend. Could someone help me get at the browser value that Sentry reports?