Hey,
thanks for creating the library

I'm suggesting to add a relative modifier to the library, which let's you align tooltips relative to element from another context
The use-case for this is aligning tooltips within iframes or on canvas (where you know the relative coordinates upfront)

Here's the modifier code:

const relative = {
  name: 'relative',
  fn: ({ x, y, element }) => {
    const rect = element.getBoundingClientRect()
    return {
      x: rect.left + x,
      y: rect.top + y
    }
  }
}

without relative modifier

with relative modifier

you can already achieve similar functionality by using virtual elements