Merge pull request #634 from creative-commoners/pulls/5/depr-validate

DOC FormField::validate() deprecation notice

Author: GuySartorelli

en/08_Changelogs/5.4.0.md

@@ -202,6 +202,7 @@ The `SilverStripe\CMS\Model\SiteTree.DESCRIPTION` localisation key (along with t
 - [`RemoteFileModalExtension::getFormSchema()`](api:SilverStripe\AssetAdmin\Extensions\RemoteFileModalExtension::getFormSchema()) has been deprecated. It will be removed without equivalent functionality to replace it.
 - [`RemoteFileModalExtension::getSchemaResponse()`](api:SilverStripe\AssetAdmin\Extensions\RemoteFileModalExtension::getSchemaResponse()) has been deprecated. It will be replaced with `RemoteFileModalExtension::getOwner()->getSchemaResponse()`.
 - [`InternalLinkModalExtension`](api:SilverStripe\CMS\Forms\InternalLinkModalExtension) has been deprecated. It will be replaced with configuration on [`ModalController`](api:SilverStripe\Admin\ModalController).
+- [`FormField::validate()`](api:SilverStripe\Forms\FormField::validate()) will take zero arguments and return a ValidationResult object instead of a boolean in CMS 6.0.0.
 
 ## Bug fixes