Share validations across models with rails 4 - validation

Question

There are other questions pertaining to this, but they all seems to be < Rails 4, and what's more, they're not too detailed!
They all talk about creating a module to share these common validations in:
require 'active_record'
module ContactValidations
def self.included(base_class)
base_class.class_eval do
include ContactValidations::InstanceMethods
# model validations
validates_presence_of(:name, :message => 'You must provide a company name.')
validates_presence_of(:street, :message => 'You must provide a company street.')
validates_presence_of(:city, :message => 'You must provide a company city.')
validates_presence_of(:post_code, :message => 'You must provide a company post code.')
validates_numericality_of(:telephone, :on => :create, :message => 'Telephone should be a number with no spaces.', :if => :telephone_given?)
validates_numericality_of(:area_code, :on => :create, :message => 'Telephone area code should be a number with no spaces.', :if => :area_code_given?)
validates_numericality_of(:fax, :on => :create, :message => 'Fax should be a number with no spaces.', :if => :fax_given?)
validates_numericality_of(:fax_area_code, :on => :create, :message => 'Fax area code should be a number with no spaces.', :if => :fax_area_code_given?)
validates_format_of(:web, :with => /^((http)?:\/\/)?(www\.)?([a-zA-Z0-9]+)(.[a-zA-Z0-9]{2,3})(\.[a-zA-Z0-9]{2,3})$/, :on => :create, :message => 'Web address is invalid. Example: http://www.domain or http://domain.', :if => :web_given?)
validates_format_of(:email, :with => /^([a-zA-Z0-9_\-\.]+)#((\[[0-9]{1,3}\.[0-9]{1,3}\.[0-9]{1,3}\.)|(([a-zA-Z0-9\-]+\.)+))([a-zA-Z]{2,4}|[0-9]{1,3})(\]?)$/, :on => :create, :message => 'Th email address given is invalid.', :if => :email_given?)
validates_uniqueness_of(:email, :message => 'This email is already given.')
end
end
module InstanceMethods
def telephone_given?
!telephone.blank?
end
def fax_given?
!fax.blank?
end
def web_given?
!web.blank?
end
def email_given?
!email.blank?
end
def area_code_given?
!area_code.blank?
end
def fax_area_code_given?
!fax_area_code.blank?
end
end
end
But I for one have no idea where such a file should be saved. In the lib directory? All files in the lib directory are included, seems a bit wasteful for a module I only want to be included in a two or three models...
Does Rails 4 have an inbuilt way to share validations?
If not, where should I save my custom module?
And just to be super clear, how should I require this module in the models that need to include these validations?

Answer 1

Create the module in app/models/concerns, then include them in your classes with:
include ContactValidations
In this way Rails will automatically load the shared modules and make them available for you to include.

Answer 2

you should also have a look at validates_with
https://api.rubyonrails.org/v6.0.3.3/classes/ActiveModel/Validations/ClassMethods.html#method-i-validates_with