toValue(str, measurement, popperOffsets, referenceOffsets) {\n  // separate value from unit\n  const split = str.match(/((?:\\-|\\+)?\\d*\\.?\\d*)(.*)/);\n  const value = +split[1];\n  const unit = split[2];\n\n  // If it's not a number it's an operator, I guess\n  if (!value) {\n    return str;\n  }\n\n  if (unit.indexOf('%') === 0) {\n    let element;\n    switch (unit) {\n      case '%p':\n        element = popperOffsets;\n        break;\n      case '%':\n      case '%r':\n      default:\n        element...