Include custom validation in BaseModel

docs/plugins/development/model-features.md

@@ -1,23 +1,51 @@
 # Model Features
 
-Plugin models can leverage certain NetBox features by inheriting from designated Python classes (documented below), defined in `netbox.models.features`. These classes perform two crucial functions:
+## Enabling NetBox Features
 
-1. Apply any fields, methods, or attributes necessary to the operation of the feature
-2. Register the model with NetBox as utilizing the feature
+Plugin models can leverage certain NetBox features by inheriting from NetBox's `BaseModel` class. This class extends the plugin model to enable numerous feature, including:
 
-For example, to enable support for tags in a plugin model, it should inherit from `TagsMixin`:
+* Custom fields
+* Custom links
+* Custom validation
+* Export templates
+* Job results
+* Journaling
+* Tags
+* Webhooks
+
+This class performs two crucial functions:
+
+1. Apply any fields, methods, or attributes necessary to the operation of these features
+2. Register the model with NetBox as utilizing these feature
+
+Simply subclass BaseModel when defining a model in your plugin:
 
 ```python
 # models.py
-from django.db.models import models
-from netbox.models.features import TagsMixin
+from netbox.models import BaseModel
 
-class MyModel(TagsMixin, models.Model):
+class MyModel(BaseModel):
     foo = models.CharField()
     ...
 ```
 
-This will ensure that TaggableManager is applied to the model, and that the model is registered with NetBox as taggable.
+## Enabling Features Individually
+
+If you prefer instead to enable only a subset of these features for a plugin model, NetBox provides a discrete "mix-in" class for each feature. You can subclass each of these individually when defining your model. (You will also need to inherit from Django's built-in `Model` class.)
+
+```python
+# models.py
+from django.db.models import models
+from netbox.models.features import ExportTemplatesMixin, TagsMixin
+
+class MyModel(ExportTemplatesMixin, TagsMixin, models.Model):
+    foo = models.CharField()
+    ...
+```
+
+The example above will enable export templates and tags, but no other NetBox features. A complete list of available feature mixins is included below. (Inheriting all the available mixins is essentially the same as subclassing `BaseModel`.)
+
+## Feature Mixins Reference
 
 !!! note
     Please note that only the classes which appear in this documentation are currently supported. Although other classes may be present within the `features` module, they are not yet supported for use by plugins.
@@ -26,6 +54,8 @@ This will ensure that TaggableManager is applied to the model, and that the mode
 
 ::: netbox.models.features.CustomFieldsMixin
 
+::: netbox.models.features.CustomValidationMixin
+
 ::: netbox.models.features.ExportTemplatesMixin
 
 ::: netbox.models.features.JobResultsMixin