wp-includes/rest-api/fields
- wp-includes/rest-api/fields/class-wp-rest-comment-meta-fields.php
- wp-includes/rest-api/fields/class-wp-rest-meta-fields.php
- wp-includes/rest-api/fields/class-wp-rest-post-meta-fields.php
- wp-includes/rest-api/fields/class-wp-rest-term-meta-fields.php
- wp-includes/rest-api/fields/class-wp-rest-user-meta-fields.php