Add a note on custom validation contexts.

The documentation on `:on` for validations was inconsistent, and most
only referenced the `:create` and `:update` contexts. I fixed those to
be consistent with the documentation on `AM::Validations.validates`,
which seemed to have the best docs.

[ci skip]

activemodel/lib/active_model/validations.rb

@@ -67,8 +67,9 @@ module ClassMethods
       #
       # Options:
       # * <tt>:on</tt> - Specifies the contexts where this validation is active.
-      #   You can pass a symbol or an array of symbols.
-      #   (e.g. <tt>on: :create</tt> or <tt>on: :custom_validation_context</tt> or
+      #   Runs in all validation contexts by default (nil). You can pass a symbol
+      #   or an array of symbols. (e.g. <tt>on: :create</tt> or
+      #   <tt>on: :custom_validation_context</tt> or
       #   <tt>on: [:create, :custom_validation_context]</tt>)
       # * <tt>:allow_nil</tt> - Skip validation if attribute is +nil+.
       # * <tt>:allow_blank</tt> - Skip validation if attribute is blank.
@@ -127,8 +128,9 @@ def validates_each(*attr_names, &block)
       #
       # Options:
       # * <tt>:on</tt> - Specifies the contexts where this validation is active.
-      #   You can pass a symbol or an array of symbols.
-      #   (e.g. <tt>on: :create</tt> or <tt>on: :custom_validation_context</tt> or
+      #   Runs in all validation contexts by default (nil). You can pass a symbol
+      #   or an array of symbols. (e.g. <tt>on: :create</tt> or
+      #   <tt>on: :custom_validation_context</tt> or
       #   <tt>on: [:create, :custom_validation_context]</tt>)
       # * <tt>:if</tt> - Specifies a method, proc or string to call to determine
       #   if the validation should occur (e.g. <tt>if: :allow_validation</tt>,

activemodel/lib/active_model/validations/validates.rb

@@ -71,9 +71,11 @@ module ClassMethods
       #
       # There is also a list of options that could be used along with validators:
       #
-      # * <tt>:on</tt> - Specifies when this validation is active. Runs in all
-      #   validation contexts by default (+nil+), other options are <tt>:create</tt>
-      #   and <tt>:update</tt>.
+      # * <tt>:on</tt> - Specifies the contexts where this validation is active.
+      #   Runs in all validation contexts by default (nil). You can pass a symbol
+      #   or an array of symbols. (e.g. <tt>on: :create</tt> or
+      #   <tt>on: :custom_validation_context</tt> or
+      #   <tt>on: [:create, :custom_validation_context]</tt>)
       # * <tt>:if</tt> - Specifies a method, proc or string to call to determine
       #   if the validation should occur (e.g. <tt>if: :allow_validation</tt>,
       #   or <tt>if: Proc.new { |user| user.signup_step > 2 }</tt>). The method,

activemodel/lib/active_model/validations/with.rb

@@ -52,8 +52,11 @@ module ClassMethods
       #   end
       #
       # Configuration options:
-      # * <tt>:on</tt> - Specifies when this validation is active
-      #   (<tt>:create</tt> or <tt>:update</tt>).
+      # * <tt>:on</tt> - Specifies the contexts where this validation is active.
+      #   Runs in all validation contexts by default (nil). You can pass a symbol
+      #   or an array of symbols. (e.g. <tt>on: :create</tt> or
+      #   <tt>on: :custom_validation_context</tt> or
+      #   <tt>on: [:create, :custom_validation_context]</tt>)
       # * <tt>:if</tt> - Specifies a method, proc or string to call to determine
       #   if the validation should occur (e.g. <tt>if: :allow_validation</tt>,
       #   or <tt>if: Proc.new { |user| user.signup_step > 2 }</tt>).

activerecord/lib/active_record/validations/associated.rb

@@ -29,9 +29,11 @@ module ClassMethods
       # Configuration options:
       #
       # * <tt>:message</tt> - A custom error message (default is: "is invalid").
-      # * <tt>:on</tt> - Specifies when this validation is active. Runs in all
-      #   validation contexts by default (+nil+), other options are <tt>:create</tt>
-      #   and <tt>:update</tt>.
+      # * <tt>:on</tt> - Specifies the contexts where this validation is active.
+      #   Runs in all validation contexts by default (nil). You can pass a symbol
+      #   or an array of symbols. (e.g. <tt>on: :create</tt> or
+      #   <tt>on: :custom_validation_context</tt> or
+      #   <tt>on: [:create, :custom_validation_context]</tt>)
       # * <tt>:if</tt> - Specifies a method, proc or string to call to determine
       #   if the validation should occur (e.g. <tt>if: :allow_validation</tt>,
       #   or <tt>if: Proc.new { |user| user.signup_step > 2 }</tt>). The method,

activerecord/lib/active_record/validations/presence.rb

@@ -44,9 +44,11 @@ module ClassMethods
       #
       # Configuration options:
       # * <tt>:message</tt> - A custom error message (default is: "can't be blank").
-      # * <tt>:on</tt> - Specifies when this validation is active. Runs in all
-      #   validation contexts by default (+nil+), other options are <tt>:create</tt>
-      #   and <tt>:update</tt>.
+      # * <tt>:on</tt> - Specifies the contexts where this validation is active.
+      #   Runs in all validation contexts by default (nil). You can pass a symbol
+      #   or an array of symbols. (e.g. <tt>on: :create</tt> or
+      #   <tt>on: :custom_validation_context</tt> or
+      #   <tt>on: [:create, :custom_validation_context]</tt>)
       # * <tt>:if</tt> - Specifies a method, proc or string to call to determine if
       #   the validation should occur (e.g. <tt>if: :allow_validation</tt>, or
       #   <tt>if: Proc.new { |user| user.signup_step > 2 }</tt>). The method, proc