This article seems to be more confusing now than helpful. A new article on lifetime is in order for Autofac 2. It's updated anyway.

Introduction

Tagged scopes are useful in applications managing components in a hierarchy of contexts with different lifetimes - e.g. Global/Request/Transaction in a web application.

It is usually only necessary to tag components whose scope matches one of the levels of the hierarchy other than the root or a leaf (e.g. Request in the example above.) This is because the root lifetime will automatically house singletons, and the leaves will by default house InstancePerLifetimeScope() or InstancePerDependency() component instances.

Tagging Components and Lifetimes

A tag can be of any type - strings or enumerations are the most common options:

builder.Register(c => new HomeController()).InMatchingLifetimeScope("request");

var container = builder.Build();
container.Tag = "application";

In this example "application" is the tag applied to the root lifetime in which singleton instances will reside, and "request" is the tag applied to the lifetime servicing HTTP requests:

// A 'request lifetime' is created for every web request
// and disposed of when the request processing completes
var requestLifetime = container.BeginLifetimeScope();
requestLifetime.Tag = "request";

Resolving Instances

In a lifetime without a matching tag or matching parent...

Each component registered for a tagged lifetime will be resolved only in that lifetime - so its child lifetimes will access instances attached to the parent. Attempting to resolve HomeController in container without creating a tagged lifetime will fail.

In a container with a matching tag...

Each requestLifetime will have a single unique instance of HomeController because of the InstancePerMatchingLifetimeScope() declaration. Default (InstancePerDependency()) components are also supported.

Further nesting...

Sub-lifetimes of requestLifetime will be able to resolve HomeController to access the single instance in their parent requestLifetime.

If default (InstancePerDependency()) scope is used, each request in a sub-lifetime will resolve a new instance, however that instance's lifetime will be bound to requestLifetime rather than the lifetime in which it is resolved.