[eyelidlessness]

You can do that with an enum!

  enum Size {
    small = 'small',
    medium = 'medium',
    large = 'large',
  }

  type ButtonProps = { size: Size.small | Size.medium }

And it’s still a nominal type in the union.

Regarding likelihood of collision, it’s easy for me to imagine mixing up 'post' in an API call to a vendor for fence materials lol. In any case I find the added safety comforting, particularly over a language where interfaces tend to be exceedingly dynamic and flexible.