No more info about dynamic_form in rails guides?

I remember for sure there was a explanation with screenshots about
dynamic_form in Rails Guides. Now I cannot find it, neither in Edge nor
in standard guide. Have they removed it? Why? Where may I find the info
again?

Wins Lin wrote in post #1113811:

I remember for sure there was a explanation with screenshots about
dynamic_form in Rails Guides. Now I cannot find it, neither in Edge nor
in standard guide. Have they removed it? Why? Where may I find the info
again?

https://github.com/joelmoss/dynamic_form

dynamic_form was included in Rails2 but stripped out of Rails3 (and 4). It’s now available as a gem.