Added doc for CustomField criterion

Author: mnocon

docs/search/criteria_reference/customfield_criterion.md

@@ -0,0 +1,27 @@
+---
+description: Custom Field Search Criterion
+---
+
+# Custom Field Criterion
+
+The [`CustomField` Search Criterion](/api/php_api/php_api_reference/classes/Ibexa-Contracts-Core-Repository-Values-Content-Query-Criterion-CustomField.html) searches for content or locations based on the contents of the search index fields.
+
+The allowed syntax and operator support might differ between search engines and the type of queried field.
+
+## Arguments
+
+- `target` - string representing the identifier of the search index field
+- `operator` - one of [Operator](/api/php_api/php_api_reference/classes/Ibexa-Contracts-Core-Repository-Values-Content-Query-Criterion-Operator.html) constants
+- `value` - the value to query for
+
+## Limitations
+
+The `CustomField` Criterion isn't available in [Repository filtering](search_api.md#repository-filtering).
+
+## Example
+
+### PHP
+
+``` php
+[[= include_file('code_samples/search/content/customfield_criterion.php') =]]
+```

docs/search/criteria_reference/search_criteria_reference.md

@@ -30,6 +30,7 @@ Due to this storage limitation, searching content using the Country field type o
 | [ContentTypeId](contenttypeid_criterion.md)                   | ID of the content item's content type                                                       | ✔       | ✔        | ✔  | ✔ |
 | [ContentTypeIdentifier](contenttypeidentifier_criterion.md)   | Identifier of the content item's content type                                               | ✔       | ✔        | ✔  |          |
 | [CurrencyCodeCriterion](currencycode_criterion.md)            | Currency code                                                                               | ✔       | ✔        | ✔  |          |
+| [CustomField](customfield_criterion.md)            | Custom field                                                                               | ✔       | ✔        |   |          |
 | [DateMetadata](datemetadata_criterion.md)                     | The date when content was created or last modified                                          | ✔       | ✔        | ✔  | ✔ |
 | [Depth](depth_criterion.md)                                   | Location depth in the content tree                                                          |                | ✔        | ✔  |          |
 | [Field](field_criterion.md)                                   | Content of one of content item's fields                                                     | ✔       | ✔        |           |          |