How to Code Display Suite Fields in Drupal

function hook_ds_fields_info($entity_type) {
 $fields = array();

 // Field definition, in this case, using technical name “title”.
 // They should be unique only within the limits of one entity and among//
 the other DS fields. So, the title here won't overlap title from the entity
 $fields['title'] = array(
   // title:  The title of the field, which will be displayed on the page of management of displayed content.// 
   'title' => t('Title'),
   // field_type: Field type
   // - DS_FIELD_TYPE_THEME      : requests theme() function.
   // - DS_FIELD_TYPE_FUNCTION   : the field result terurns as a function.
   'field_type' => DS_FIELD_TYPE_FUNCTION,
   // ui_limit: Allows you to specify in which variants of display within the entity limits the field is defined for // field will be accessible for use in the following format: $bundle|$view_mode.  You can replace some parts with *, this way
   // specifying what will be accessible in all variants. 
   'ui_limit' => array('article|full', '*|teaser'),
   // file: The path to a file which contents the code is specified here. It's used only
  //for DS_FIELD_TYPE_FUNCTION  type. The path should be full, for example:
   // drupal_get_path('module', 'MYMODULE') . '/inc/file.inc',
   'file' => 'optional_filename',
   // function: The function name which will return the result for
   //  a field. Only for DS_FIELD_TYPE_FUNCTION type.
   'function' => 'theme_ds_title_field',
   // properties: Additional field settings.
   'properties' => array(
     // formatters: optionally for the function and required for
     // DS_FIELD_TYPE_THEME. By the way, for the second one, you should also // // //register the theming function via hook_theme()
//if it’s not present. It will be requested as  theme('function');
     //In this array, the key is a function of theme(), and the value is only a tag for something in// the admin panel. It will be a select where you can choose the output format.      'formatters' => array(
       'node_title_nolink_h1' => t('H1 title'),
       'node_title_link_h1' => t('H1 title, linked to node'),
     ),
     // settings & default: Optionally, used only if you want
     // to add some field settings which will be present in UI.
     'settings' => array(
       'wrapper' => array(
         'type' => 'textfield',
         'description' => t('Eg: h1, h2, p'),
       ),
       'link' => array(
         'type' => 'select',
         'options' => array('yes', 'no'),
       ),
     ),
     'default' => array(
       'wrapper' => 'h2',
       'link' => 0,
     ),
   ),
 );

 return array('node' => $fields);
}

/**
* Implements hook_ds_fields_info().
*/
function mymodule_ds_fields_info($entity_type) {
 $fields = array();

 if ($entity_type == 'node') {
   $fields['word_count'] = array(
     'title' => 'DS: The number of words in the text',
     'field_type' => DS_FIELD_TYPE_FUNCTION,
     //  We need this field only in a full format of displaying article material
     'ui_limit' => array('article|full'),
     // The function name
     'function' => 'mymodule_ds_field_word_count',
   );

   return array($entity_type => $fields);
 }
 return;
}
/**
* The function which will be requested and return the result to the field. 
* If the function returns nothing, false or null, it's 
*considered as an empty field, and it won't be rendered.
*
* @param $field
*  It contains all necessary information for us.
*/
function mymodule_ds_field_word_count($field) {
 // The entity object, which this field was requested for, is contained in
 // $field['entity']. For simplicity and clearness of code we use EMW.
 $entity_wrapper = entity_metadata_wrapper('node', $field['entity']);

 if ($body_value = $entity_wrapper->body->value->value()) {
   // Returning of result.
   return format_string(
     '<strong>The number of worts in the text:</strong> @word_count',
     array(
       '@word_count' => str_word_count(strip_tags($body_value))
     )
   );
 }
}

namespace DrupalmymodulePluginDsField;

use DrupaldsPluginDsFieldDsFieldBase;
use DrupalComponentRenderFormattableMarkup;
/**
* The field which outputs the number of words in the content.
*
* @DsField(
*   id = "word_count",
*   title = @Translation("DS: Word count"),
*   provider = "mymodule",
*   entity_type = "node",
*   ui_limit = {"article|full"}
* )
*/
class WordCount extends DsFieldBase {
 /**
  * {@inheritdoc}
  *
  * The method which should return the result to the field.
  */
 public function build() {
   // Writing the object of the current entity into a variable for the convenience
   $entity = $this->entity();
   // Check if there is a value in a body field. If the field returnes nothing
   // it takes like empty field and it isn't outputed. 
   if ($body_value = $entity->body->value) {
     return [
       '#type' => 'markup',
       '#markup' => new FormattableMarkup(
         '<strong>?????????? ???? ? ??????:</strong> @word_count',
         [
           '@word_count' => str_word_count(strip_tags($body_value))
         ]
       )
     ];
   }
 }
}