code: function isOutside (feature, poly) {
    var a = feature.bbox = feature.bbox || extent(feature)
    var b = poly.bbox = poly.bbox || extent(poly)
    return a[2] < b[0] || a[0] > b[2] || a[3] < b[1] || a[1] > b[3]
  }
docs: no false positives, some false negatives