Merge pull request rails#47838 from p8/docs/headers-activemodel2

Fix more missing Active Model documentation headers

Author: p8

activemodel/lib/active_model/error.rb

@@ -3,7 +3,7 @@
 require "active_support/core_ext/class/attribute"
 
 module ActiveModel
-  # == Active \Model \Error
+  # = Active \Model \Error
   #
   # Represents one single error
   class Error

activemodel/lib/active_model/errors.rb

@@ -472,6 +472,8 @@ def normalize_arguments(attribute, type, **options)
       end
   end
 
+  # = Active \Model \Validator
+  #
   # Raised when a validation cannot be corrected by end users and are considered
   # exceptional.
   #
@@ -490,10 +492,14 @@ def normalize_arguments(attribute, type, **options)
   class StrictValidationFailed < StandardError
   end
 
+  # = Active \Model \RangeError
+  #
   # Raised when attribute values are out of range.
   class RangeError < ::RangeError
   end
 
+  # = Active \Model \UnknownAttributeError
+  #
   # Raised when unknown attributes are supplied via mass assignment.
   #
   #   class Person

activemodel/lib/active_model/forbidden_attributes_protection.rb

@@ -1,6 +1,8 @@
 # frozen_string_literal: true
 
 module ActiveModel
+  # = Active \Model \ForbiddenAttributesError
+  #
   # Raised when forbidden attributes are used for mass assignment.
   #
   #   class Person < ActiveRecord::Base

activemodel/lib/active_model/validator.rb

@@ -124,6 +124,8 @@ def validate(record)
     end
   end
 
+  # = Active \Model \EachValidator
+  #
   # +EachValidator+ is a validator which iterates through the attributes given
   # in the options hash invoking the <tt>validate_each</tt> method passing in the
   # record, attribute, and value.