Improve docs

Author: brendt

src/Web/Documentation/content/main/1-framework/12-validation.md

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+---
+title: Validation
+category: framework
+---
+
+Validation with Tempest is done by taking an array of raw input data, and validating whether that array of data is valid against a class. While validation and [data mapping](/main/framework/validation) often work together, the two are separate components and can also be used separately.
+
+Here's an object that can be validated:
+
+```php
+final class Book
+{
+    public string $title;
+
+    public string $description;
+
+    public ?DateTimeImmutable $publishedAt = null;
+}
+```
+
+As you can see, there are no explicit validation rules, that's because Tempest will first look at the object's type definitions and infer validation rules based on those: `$title` and `$description` are required since these aren't nullable properties, they should both be text; `$publishedAt` is optional, and it expects a valid date time string.
+
+Validating an array of data against this `Book` object would look like this:
+
+```php
+use Tempest\Validation\Validator;
+
+$validator = new Validator();
+
+$failingRules = $validator->validateValuesForClass(Book::class,  [
+    'title' => 'Timeline Taxi',
+    'description' => 'My sci-fi novel',
+    'publishedAt' => '2024-10-01',
+]);
+```
+
+If validation fails, `$failingRules` will contain a list of fields and their respective failed rules.
+
+## Validation Rules
+
+As mentioned before, the validator makes use of rules to validate an array of data against a class. While the validator will infer some rules based on property types, there are a whole lot more that can be added via attributes:
+
+```php
+use Tempest\Validation\Rules\Length;
+use Tempest\Validation\Rules\NotEmpty;
+use Tempest\Validation\Rules\DateTimeFormat;
+
+final class Book
+{
+    #[Length(min: 5, max: 50)]
+    public string $title;
+
+    #[NotEmpty]
+    public string $description;
+    
+    #[DateTimeFormat('Y-m-d')]
+    public ?DateTimeImmutable $publishedAt = null;
+}
+```
+
+A list of all available validation rules can be found on [GitHub](https://github.com/tempestphp/tempest-framework/tree/main/src/Tempest/Validation/src/Rules). 
+
+## Skipping Validation
+
+Some properties should never be validated. You can use the `#[SkipValidation]` attribute to exclude them from the validator:
+
+```php
+use Tempest\Validation\SkipValidation;
+
+final class Book
+{
+    #[SkipValidation]
+    public string $title;
+}
+```