code: function isSimplePath (exp) {
    return pathTestRE.test(exp) &&
      // don't treat true/false as paths
      !booleanLiteralRE.test(exp) &&
      // Math constants e.g. Math.PI, Math.E etc.
      exp.slice(0, 5) !== 'Math.'
  }
docs: Check if an expression is a simple path.
  
  @param {String} exp
  @return {Boolean}