  * @param {string|RegExp} url HTTP url.  * @param {(string|RegExp)=} data HTTP request body.  * @param {(Object|function(Object))=} headers HTTP headers or function that receives http header  *   object and returns true if the headers match the current definition.  * @returns {requestHandler} Returns an object with `respond` and `passThrough` methods that  *   control how a matched request is handled.  *