What is concern and when, why does it use in rails?

[sdubois (Sébastien Dubois)]

This new section in the getting started guide might be helpful.

Getting Started with Rails — Ruby on Rails Guides

See prior discussion:

Helping devs understand concerns faster

One thing that took me a while to wrap my head around is concerns. Part of that is just that I hadn’t really used them before and they’re more of a Ruby (and Rails) thing that with other languages. At the same time, they’re SUPER powerful and helpful. It feels like people could see the power of Rails better if they understood Rails and concerns. There are a set of things that could help with this: Putting a concern focused guide together on guides.rubyonrails.org. There are a number of places…

Add Concerns section in Refactoring portion of Getting Started guide