edit.routing.yml

EditController::fieldForm in drupal/core/modules/edit/lib/Drupal/edit/EditController.php

Returns a single field edit form as an Ajax response.

edit_menu in drupal/core/modules/edit/edit.module

Implements hook_menu().

edit_metadata:
  pattern: '/edit/metadata'
  defaults:
    _controller: '\Drupal\edit\EditController::metadata'
  requirements:
    _permission: 'access in-place editing'

edit_attachments:
  pattern: '/edit/attachments'
  defaults:
    _controller: '\Drupal\edit\EditController::attachments'
  requirements:
    _permission: 'access in-place editing'

edit_field_form:
  pattern: '/edit/form/{entity_type}/{entity}/{field_name}/{langcode}/{view_mode_id}'
  defaults:
    _controller: '\Drupal\edit\EditController::fieldForm'
  requirements:
    _permission: 'access in-place editing'
    _access_edit_entity_field: 'TRUE'