code: func (i *Image) Fill(spec string) (*Image, error) {
  	return i.doWithImageConfig("fill", spec, func(src image.Image, conf imageConfig) (image.Image, error) {
  		if conf.AnchorStr == smartCropIdentifier {
  			return smartCrop(src, conf.Width, conf.Height, conf.Anchor, conf.Filter)
  		}
  		return imaging.Fill(src, conf.Width, conf.Height, conf.Anchor, conf.Filter), nil
  	})
  }
docs: // Fill scales the image to the smallest possible size that will cover the specified dimensions,
  // crops the resized image to the specified dimensions using the given anchor point.
  // Space delimited config: 200x300 TopLeft