add docs about payment/shipping provider settings validation

Author: umbracotrd

16/umbraco-commerce/key-concepts/payment-providers.md

@@ -35,10 +35,28 @@ public class MyPaymentProviderSettings
 
 All Payment Providers inherit from a base class `AsyncPaymentProviderBase<TSettings>`. `TSettings` is the type of a Plain Old Class Object (POCO) model class representing the Payment Provider's settings. The class must be decorated with `PaymentProviderAttribute` which defines the Payment Providers `alias`.
 
+### Payment Provider Settings
 The settings class consists of a series of properties, each decorated with a `PaymentProviderSettingAttribute`. These will all be used to dynamically build an editor interface for the given settings in the backoffice.
 
 Labels and descriptions for providers and their settings are controlled through [Localization](#localization) entries.
 
+{% hint style="info" %}
+The **Validate Payment Provider Settings** feature has been available since Umbraco Commerce 16.4.0.
+{% endhint %}
+
+Umbraco Commerce supports validating payment provider settings by using `System.ComponentModel.DataAnnotations.ValidationAttribute`.
+
+```csharp
+public class MyPaymentProviderSettings
+{
+    [System.ComponentModel.DataAnnotations.Required] // Validation Attribute
+    [System.ComponentModel.DataAnnotations.StringLength(100)] // Validation Attribute
+    [PaymentProviderSetting(SortOrder = 100)]
+    public string ContinueUrl { get; set; }
+    ...
+}
+```
+
 ## Payment Provider Responsibilities
 
 There are two main responsibilities of a Payment Provider, and those are:

16/umbraco-commerce/key-concepts/shipping-providers.md

@@ -35,10 +35,27 @@ public class MyShippingProviderSettings
 
 All Shipping Providers inherit from a base class `ShippingProviderBase<TSettings>`. `TSettings` is the type of a Plain Old Class Object (POCO) model class representing the Shipping Provider's settings. The class must be decorated with `ShippingProviderAttribute` which defines the Shipping Providers `alias`.
 
+### Shipping Provider Settings
 The settings class consists of a series of properties, each decorated with a `ShippingProviderSettingAttribute`. These will all be used to dynamically build an editor interface for the given settings in the backoffice.
 
 Labels and descriptions for providers and their settings are controlled through [Localization](#localization) entries.
 
+{% hint style="info" %}
+The **Validate Shipping Provider Settings** feature has been available since Umbraco Commerce 16.4.0.
+{% endhint %}
+
+Umbraco Commerce supports validating shipping provider settings by using `System.ComponentModel.DataAnnotations.ValidationAttribute`.
+
+```csharp
+public class MyShippingProviderSettings
+{
+    [System.ComponentModel.DataAnnotations.Required] // Validation Attribute
+    [System.ComponentModel.DataAnnotations.StringLength(100)] // Validation Attribute
+    [ShippingProviderSetting(SortOrder = 100)]
+    public string ContinueUrl { get; set; }
+    ...
+}
+```
 ## Shipping Provider Responsibilities
 
 The responsibilities of a Shipping Provider are: