What does the “mount” instruction mean in Rails routing?

Question

I cannot find the meaning of the keyword "mount" in Rails routing system .

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I have set up Mercury to use within my Rails application. It added this line to my routes.rb config file:

Appname::Application.routes.draw do
  mount Mercury::Engine => '/'

What does the mount keyword mean?

Answer 1

Mount within the Rails routes does the equivalent of a Unix mount .
It actually tells the app that another application (usually a Rack application) exists on that location.

It is used mostly for Rails Engines.

Answer 2

Mounting an engine means that the functionality from that engine is available inside your application.

See http://guides.rubyonrails.org/engines.html#mounting-the-engine