code: @Override
  	public MetricsPlugin register(RestExpress server)
  	{
  		if (isRegistered) return this;
  
  		server.registerPlugin(this);
  		this.isRegistered = true;
  
  		server
  			.addMessageObserver(this)
  			.addPreprocessor(this)
  			.addFinallyProcessor(this);
  
  		return this;
  	}
docs: Register the MetricsPlugin with the RestExpress server.
  
  @param server a RestExpress server instance.
  @return MetricsPlugin