doc (external-vocabularies): guess IRI from validation constraints

Author: GregoireHebert

core/external-vocabularies.md

@@ -55,3 +55,23 @@ The generated JSON for products and the related context document will now use ex
 ```
 
 An extended list of existing open vocabularies is available on [the Linked Open Vocabularies (LOV) database](http://lov.okfn.org/dataset/lov/).
+
+By default, when using [validations](validation.md) API Platform Core will try to define known [Schema.org](https://schema.org) types as IRIs for your properties if you did not provide any in your `@ApiProperty` annotations.
+Built-in mapping is:
+
+Constraints                                          | Schema.org type                   |
+---------------------------------------------------- |-----------------------------------|
+`Symfony\Component\Validator\Constraints\Url`        | `http://schema.org/url`           |
+`Symfony\Component\Validator\Constraints\Email`      | `http://schema.org/email`         |
+`Symfony\Component\Validator\Constraints\Uuid`       | `http://schema.org/identifier`    |
+`Symfony\Component\Validator\Constraints\CardScheme` | `http://schema.org/identifier`    |
+`Symfony\Component\Validator\Constraints\Bic`        | `http://schema.org/identifier`    |
+`Symfony\Component\Validator\Constraints\Iban`       | `http://schema.org/identifier`    |
+`Symfony\Component\Validator\Constraints\Date`       | `http://schema.org/Date`          |
+`Symfony\Component\Validator\Constraints\DateTime`   | `http://schema.org/DateTime`      |
+`Symfony\Component\Validator\Constraints\Time`       | `http://schema.org/Time`          |
+`Symfony\Component\Validator\Constraints\Image`      | `http://schema.org/image`         |
+`Symfony\Component\Validator\Constraints\File`       | `http://schema.org/MediaObject`   |
+`Symfony\Component\Validator\Constraints\Currency`   | `http://schema.org/priceCurrency` |
+`Symfony\Component\Validator\Constraints\Isbn`       | `http://schema.org/isbn`          |
+`Symfony\Component\Validator\Constraints\Issn`       | `http://schema.org/issn`          |