What does the first argument 0 or 1 mean for glbinding::initialize() function call in multi context application?

[asmwarrior]

There is a document section Multi-Context Support, which mentions how to use multi contexts. Also multi contexts sample code are here.

In the code, I see:

glbinding/source/examples/multi-context/main.cpp

Lines 58 to 88 in 6ae6961

	GLFWwindow * window1 = glfwCreateWindow(640, 480, "", nullptr, nullptr);
	if (!window1)
	{
	glfwTerminate();
	return -1;
	}
	glfwSetKeyCallback(window1, key_callback);
	glfwMakeContextCurrent(window1);
	glbinding::initialize(0, glfwGetProcAddress, false); // only resolve functions that are actually used (lazy)
	glbinding::aux::enableGetErrorCallback();
	// Initialize window 2
	GLFWwindow * window2 = glfwCreateWindow(640, 480, "", nullptr, nullptr);
	if (!window2)
	{
	glfwTerminate();
	return -1;
	}
	glfwMakeContextCurrent(window2);
	glfwSetKeyCallback(window2, key_callback);
	glbinding::initialize(1, glfwGetProcAddress, false); // only resolve functions that are actually used (lazy)
	glbinding::aux::enableGetErrorCallback();
	// print some gl infos (query)

You can see, the first argument of initialize() is either 0 or 1 for different OpenGL context. What dose the 0 and 1 mean?

Can I just use a unique int number for this argument?