DOC Update typehints in docs (#569)

en/02_Developer_Guides/01_Templates/01_Syntax.md

@@ -575,7 +575,7 @@ use Page;
 
 class HomePage extends Page
 {
-    public function forTemplate()
+    public function forTemplate(): string
     {
         // We can also render a template here using $this->renderWith()
         return 'Page: ' . $this->Title;

en/02_Developer_Guides/15_Customising_the_Admin_Interface/04_Preview.md

@@ -284,7 +284,7 @@ class Product extends DataObject implements CMSPreviewable
 {
     // ...
 
-    public function forTemplate()
+    public function forTemplate(): string
     {
         // If the template for this DataObject is not an "Include" template, use the appropriate type here
         // e.g. "Layout".

en/08_Changelogs/6.0.0.md

@@ -11,14 +11,16 @@ title: 6.0.0 (unreleased)
   - [Changes to default cache adapters](#caching)
   - [Changes to scaffolded form fields](#scaffolded-fields)
   - [`SiteTree` uses form field scaffolding](#sitetree-scaffolding)
-  - [Other new features](#other-new-features)
+  - [Changes to the templating/view layer](#view-layer)
+  - [Other new features and small changes](#other-new-features)
 - [Dependency changes](#dependency-changes)
   - [`intervention/image` has been upgraded from v2 to v3](#intervention-image)
 - [Bug fixes](#bug-fixes)
 - [API changes](#api-changes)
   - [Most extension hook methods are now protected](#hooks-protected)
   - [Strict typing for `Factory` implementations](#factory-strict-typing)
   - [General changes](#api-general)
+- [Full list of removed and changed API (by module, alphabetically)](#api-removed-and-changed)
 
 ## Features and enhancements
 
@@ -181,12 +183,27 @@ SilverStripe\UserForms\Model\UserDefinedForm:
 
 </details>
 
-### Other new features
+### Changes to the templating/view layer {#view-layer}
 
-- Native indexed PHP arrays can now be passed into templates and iterated over with `<% loop $MyArray %>`. Under the hood they are wrapped in [`ArrayList`](api:SilverStripe\View\ViewableData), so you can get the count using `$Count` and use `<% if $ArrayList %>` as a shortcut for `<% if $ArrayList.Count %>`. Other functionality from `ArrayList` such as filtering and sorting cannot be used on arrays since they don't have keys to filter or sort against.
+#### Strong typing for `ViewableData` and `DBField`
+
+Many of the properties and methods in [`ViewableData`](api:SilverStripe\View\ViewableData), [`DBField`](api:SilverStripe\ORM\FieldType\DBField), and their immediate subclasses have been given strong typehints. Previously, these only had typehints in the PHPDoc which meant that any arbitrary values could be assigned or returned.
+
+Most of the strong types are either identical to the old PHPDoc types, or match what was already actually being assigned to, passed into, and returned from those APIs.
+
+In some cases, where a string was expected but sometimes `null` was being used, we have explicitly strongly typed the API to `string`. This matches [similar changes PHP made in PHP 8.1](https://php.watch/versions/8.1/internal-func-non-nullable-null-deprecation) and will help avoid passing `null` values in to functions that expect a string.
+
+The one change we specifically want to call out is for [`ViewableData::obj()`](api:SilverStripe\View\ViewableData::obj()). This method will now explicitly return `null` if there is no field, property, method, etc to represent the field you're trying to get an object for. This is a change from the old behaviour, where an empty `DBField` instance would be returned even though there's no way for any non-null value to be available for that field.
+
+See the [full list of removed and changed API](#api-removed-and-changed) to see all of the API with updated typing.
+
+### Other new features and small changes {#other-new-features}
+
+- Native indexed PHP arrays can now be passed into templates and iterated over with `<% loop $MyArray %>`. Under the hood they are wrapped in [`ArrayList`](api:SilverStripe\ORM\ArrayList), so you can get the count using `$Count` and use `<% if $ArrayList %>` as a shortcut for `<% if $ArrayList.Count %>`. Other functionality from `ArrayList` such as filtering and sorting cannot be used on arrays since they don't have keys to filter or sort against.
 - Modules no longer need to have a root level `_config.php` or `_config` directory to be recognised as a Silverstripe CMS module. They will now be recognised as a module if they have a `composer.json` file with a `type` of `silverstripe-vendormodule` or `silverstripe-theme`.
 - A new [`DataObject::getCMSEditLink()`](api:SilverStripe\ORM\DataObject::getCMSEditLink()) method has been added, which returns `null` by default. This provides more consistency for that method which has previously been inconsistently applied to various subclasses of `DataObject`. See [managing records](/developer_guides/model/managing_records/#getting-an-edit-link) for more details about providing sane values for this method in your own subclasses.
 - The `CMSEditLink()` method on many `DataObject` subclasses has been renamed to `getCMSEditLink()`.
+- Previously if an invalid default value was provided for a [`DBDecimal`](api:SilverStripe\ORM\FieldType\DBDecimal) database column, it would silently set the defalt value to `0`. This will now throw an exception instead, so that you're aware your configured value is invalid and can correct it.
 
 ## Dependency changes
 
@@ -322,6 +339,8 @@ Injector::inst()->load([
 - [`FieldList`](api:SilverStripe\Forms\FieldList) is now strongly typed. Methods that previously allowed any iterable variables to be passed, namely [`FieldList::addFieldsToTab()`](api:SilverStripe\Forms\FieldList::addFieldsToTab()) and [`FieldList::removeFieldsFromTab()`](api:SilverStripe\Forms\FieldList::removeFieldsFromTab()), now require an array to be passed instead.
 - [`BaseElement::getDescription()`](api:DNADesign\Elemental\Models\BaseElement::getDescription()) has been removed. If you had implemented this method in your custom elemental blocks, either set the [`description`](api:DNADesign\Elemental\Models\BaseElement->description) configuration property or override the [`getTypeNice()`](api:DNADesign\Elemental\Models\BaseElement::getTypeNice()) method.
 
+### Full list of removed and changed API (by module, alphabetically) {#api-removed-and-changed}
+
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