function Readability(doc, options) {
  // In some older versions, people passed a URI as the first argument. Cope:
  if (options && options.documentElement) {
    doc = options;
    options = arguments[2];
  } else if (!doc || !doc.documentElement) {
    throw new Error("First argument to Readability constructor should be a document object.");
  }
  options = options || {};

  this._doc = doc;
  this._docJSDOMParser = this._doc.firstChild.__JSDOMParser__;
  this._articleTitle = null;
  this._articleByline = null;
  this._articleDir = null;
  this._articleSiteName = null;
  this._attempts = [];

  // Configurable options
  this._debug = !!options.debug;
  this._maxElemsToParse = options.maxElemsToParse || this.DEFAULT_MAX_ELEMS_TO_PARSE;
  this._nbTopCandidates = options.nbTopCandidates || this.DEFAULT_N_TOP_CANDIDATES;
  this._charThreshold = options.charThreshold || this.DEFAULT_CHAR_THRESHOLD;
  this._classesToPreserve = this.CLASSES_TO_PRESERVE.concat(options.classesToPreserve || []);
  this._keepClasses = !!options.keepClasses;
  this._serializer = options.serializer || function(el) {
    return el.innerHTML;
  };
  this._disableJSONLD = !!options.disableJSONLD;
  this._allowedVideoRegex = options.allowedVideoRegex || this.REGEXPS.videos;

  // Start with all flags set
  this._flags = this.FLAG_STRIP_UNLIKELYS |
                this.FLAG_WEIGHT_CLASSES |
                this.FLAG_CLEAN_CONDITIONALLY;


  // Control whether log messages are sent to the console
  if (this._debug) {
    let logNode = function(node) {
      if (node.nodeType == node.TEXT_NODE) {
        return `${node.nodeName} ("${node.textContent}")`;
      }
      let attrPairs = Array.from(node.attributes || [], function(attr) {
        return `${attr.name}="${attr.value}"`;
      }).join(" ");
      return `<${node.localName} ${attrPairs}>`;
    };
    this.log = function () {
      if (typeof console !== "undefined") {
        let args = Array.from(arguments, arg => {
          if (arg && arg.nodeType == this.ELEMENT_NODE) {
            return logNode(arg);
          }
          return arg;
        });
        args.unshift("Reader: (Readability)");
        console.log.apply(console, args);
      } else if (typeof dump !== "undefined") {
        /* global dump */
        var msg = Array.prototype.map.call(arguments, function(x) {
          return (x && x.nodeName) ? logNode(x) : x;
        }).join(" ");
        dump("Reader: (Readability) " + msg + "\n");
      }
    };
  } else {
    this.log = function () {};
  }
}
Public constructor.
@param {HTMLDocument} doc     The document to parse.
@param {Object}       options The options object.