Talked with @fxn about this. Bullet points should have periods at the ends.

The wording of these was a bit off, so I fixed them.

The proper name has a space.

The proper name has a space.

The proper name has a space.

The proper name for the library has a space.

The proper name has a space.

The proper name, as per the documentation guides, is 'Active Record.' I've
updated several references to it as 'ActiveRecord'.

Most of the guides have a few simple sentences describing what they will show
you at the top. This one had a few big paragraphs. I've moved those paragraphs
down to an introductory one, and written a new smaller one for the introduction.
This makes this guide more consistent with the others.

It's properly called "Mac OS X"

This is based on Rails 4, not Rails 3.2.

Revert "correct css selector for the display of validation error messages: changed #error_explanation to #errorExplanation"

At least in master the selector is snake case.

This reverts commit ba2fed41.

From https://github.com/lifo/docrails/commit/cfd324b4b68469ba3188e4b7ba8586e59b239693\#commitcomment-2213592

From https://github.com/rails/rails/issues/6161\#issuecomment-10750118

correct css selector for the display of validation error messages: changed #error_explanation to #errorExplanation

Clarification to ActiveRecord Validations Doc in 7.2 Custom Methods

In the expiration_date_cannot_be_in_the_past validation method, use `expiration_date.present?` instead of the double negative `!expiration_date.blank?`. Also join the comparisons with `&&` instead of `and`, which could cause unintended consequences.

This reverts commit c94cfdad.

* This is the new 4.0 (master) directory structure

* This shows the reader there is a method: and 
  data: parameters

* No need to give a simple example, as we have a
  partial that we create in the blog app

* Rails generate model Post ______ creates the
  attr_accessible line for you for any fields
  you specify. Changed the section to describe
  what this line in the model does.

prevent mass assignment of polymorphic type when using `build`

Conflicts:
	activerecord/CHANGELOG.md

[ci skip]

Allow setting a symbol as path in scope on routes

Closes #8265

Was surprising found that this example doesn't work:

  scope :api do
    resources :users
  end

and the right form to use it is:

  scope 'api' do
    resources :users
  end

I think this should work similary as `namespace` where both are allowed.
These two are equivalent:

  namespace :api do
    resources :users
  end

  namespace 'api' do
    resources :user
  end

Since now these objects are not cached anymore, there's no need to have
these private methods, just instantiate each of them in the necessary
place.

Follow up of the discussion from the original merge commit:
https://github.com/rails/rails/commit/f9cb645dfcb5cc89f59d2f8b58a019486c828c73#commitcomment-1414561

We want to avoid people's mistakes with methods like count and sum when
called with a block, that can easily lead to code performing poorly and
that could be way better written with a db query.

Please check the discussion there for more background.
Closes #8268

Since edd94cee, CollectionProxy
delegates all calculation methods - except count - to the scope,
which does basically what this method was doing, but since we're
delegating from the proxy, the association method was never called.