class FieldUpdateForbiddenException

field.api.php in drupal/core/modules/field/field.api.php

field_sql_storage.module in drupal/core/modules/field/modules/field_sql_storage/field_sql_storage.module

Default implementation of the field storage API.

options.module in drupal/core/modules/field/modules/options/options.module

Defines selection, check box and radio button widgets for text and numeric fields.

class FieldUpdateForbiddenException extends FieldException {

}