`http.ClientRequest` poor documentation

I'm using tj's superagent, and I want to inspect the actual url requesting

var request = require('superagent');

request
   .get('<some url>')
   .on('request',function(){
        var req = this.req; // req instanceof http.ClientRequest
    })
   .end(function(err,res){

    })

req instanceof http.ClientRequest, but I can hardly find any property reference in the documentation on http.ClientRequest class https://iojs.org/api/http.html#http_class_http_clientrequest