code: function createEndpointRequest( handlerSpec, resource, namespace ) {
  
  	// Create the constructor function for this endpoint
  	class EndpointRequest extends WPRequest {
  		constructor( options ) {
  			super( options );
  
  			/**
  			 * Semi-private instance property specifying the available URL path options
  			 * for this endpoint request handler, keyed by ascending whole numbers.
  			 *
  			 * @property _levels
  			 * @type {object}
  			 * @private
  			 */
  			this._levels = handlerSpec._levels;
  
  			// Configure handler for this endpoint's root URL path & set namespace
  			this
  				.setPathPart( 0, resource )
  				.namespace( namespace );
  		}
  	}
  
  	// Mix in all available shortcut methods for GET request query parameters that
  	// are valid within this endpoint tree
  	if ( typeof handlerSpec._getArgs === 'object' ) {
  		Object.keys( handlerSpec._getArgs ).forEach( ( supportedQueryParam ) => {
  			const mixinsForParam = mixins[ supportedQueryParam ];
  
  			// Only proceed if there is a mixin available AND the specified mixins will
  			// not overwrite any previously-set prototype method
  			if ( typeof mixinsForParam === 'object' ) {
  				Object.keys( mixinsForParam ).forEach( ( methodName ) => {
  					applyMixin( EndpointRequest.prototype, methodName, mixinsForParam[ methodName ] );
  				} );
  			}
  		} );
  	}
  
  	Object.keys( handlerSpec._setters ).forEach( ( setterFnName ) => {
  		// Only assign setter functions if they do not overwrite preexisting methods
  		if ( ! EndpointRequest.prototype[ setterFnName ] ) {
  			EndpointRequest.prototype[ setterFnName ] = handlerSpec._setters[ setterFnName ];
  		}
  	} );
  
  	return EndpointRequest;
  }
docs: Create an endpoint request handler constructor for a specific resource tree
  
  @method create
  @param {Object} handlerSpec A resource handler specification object
  @param {String} resource    The root resource of requests created from the returned factory
  @param {String} namespace   The namespace string for the returned factory's handlers
  @returns {Function} A constructor inheriting from {@link WPRequest}