Running Rails as an embedded app inside of a gem

I'm trying to understand what exactly the above (in my question's Title) means? This is taken directly from the SpreeCommerce.com project:

If you’re an experienced Rails developer you may be wondering where your app directory is. Spree actually runs as an embedded Rails app inside of your gem. How do you customize things then? We’ll cover that later in extensions.

So开发者_Go百科urce: http://spreecommerce.com/documentation/getting_started.html

Can someone further explain what exactly it means when a Rails app is run "inside of your gem"

With the gem spree, you can install your application and use it. A lot of application need download complete package to install it. When the gem spree, you don't. So it's more easier to install spree on your server.

The phrase you quote is poorly written and not particularly useful. What you should take away is that Spree is structured different from the majority of Rails plugins.

Typical plugin:

your rails app <-- plugin functionality

A Spree app:

spree rails app <-- your site specific code

Typically, most Rails plugins are installed in the vendor/plugins directory of your Rails app. Some additional functionality is added by classes and modules that you can then reference in your code (subclassing a ResourceController, for instance).

Spree does not work in this way. Because, presumably, there is so much configuration code for Spree, each Spree instance creates a separate Rails app -- one that's missing some of the more important parts of a Rails app (such as the app directory). All of your site specific code goes in the vendor/extensions/site directory. This means you don't have to worry about editing any of the Spree-specific code (since it's all in a different directory) and you can more easily put your own code under source control.