Quick example of inline validator (original doc did not mention inline validator)

docs/guide/validation.md

@@ -110,6 +110,19 @@ Validates that the attribute value is among a list of values.
 - `strict` whether the comparison is strict (both type and value must be the same). _(false)_
 - `not` whether to invert the validation logic. _(false)_
 
+### `inline`: [[InlineValidator]]
+
+Uses a custom function to validate the attribute. You need to define a public method in your model class which will evaluate the validity of the attribute. For example, if an attribute needs to be divisible by 10. In the rules you would define: `['attributeName', 'myValidationMethod'],`.
+
+Then, your own method could look like this:
+```php
+public function myValidationMethod($attribute) {
+    if(($attribute % 10) != 0) {
+         $this->addError($attribute, 'cannot divide value by 10');
+    }
+}
+```
+
 ### `integer`: [[NumberValidator]]
 
 Validates that the attribute value is an integer number.