docs: function qexp(rate, lowerTail, logp) {
        logp = logp === true;
        lowerTail = lowerTail !== false;
  
        if (utils.hasNaN(rate)) { return function(x) { return NaN; }; }
  
        return utils.qhelper(lowerTail, logp, 0, Infinity, function(p) {
           if (rate < 0 && rate !== -Infinity) { return NaN; }
           if (logp) {
              return lowerTail ? -Math.log(-expm1(p)) / rate
                               : -p / rate;
           }
           return lowerTail ? -log1p(-p) / rate
                            : -Math.log(p) / rate;
        });
     }