code: function createOverride(sXHRMethod) {
  
  		mRegistry[sXHRMethod] = Object.create(null);
  
  		//  backup the original function
  		mXHRFunctions[sXHRMethod] = window.XMLHttpRequest.prototype[sXHRMethod];
  
  		window.XMLHttpRequest.prototype[sXHRMethod] = function() {
  			var oArgs = arguments;
  
  			// call the original function first
  			mXHRFunctions[sXHRMethod].apply(this, oArgs);
  
  			// call the registered callbacks in order of their registration
  			for (var sName in mRegistry[sXHRMethod]) {
  				mRegistry[sXHRMethod][sName].apply(this, oArgs);
  			}
  
  		};
  
  	}
docs: Creates the initial override for an original XHR method.
  
  @param {string} sXHRMethod Name of the actual XHR method
  @param {function} fnCallback The registered callback function
  @private