Custom DS fields example (remove .php from filename, only for github code highlighter)

somemodule.module.php

<?php

function somemodule_ds_fields_info($entity_type) {
  $fields = array();
  $fields['node']['some_field'] = array(
    // Arbitrary UI label.
    'title' => t('Some field'),
    // DS constant for field type function.
    'field_type' => DS_FIELD_TYPE_FUNCTION,
    // Name of the actual function.
    'function' => 'somemodule_some_field',
    // Optional file the function resides in.
    // 'file' => drupal_get_path('module', 'somemodule') . '/includes/ds.fields.inc',
    // Limits on availability. Replace "node_type" with the type of node and "view_mode" with the view mode,
    // wildcards(*) are available.
    'ui_limit' => array(
      'some_type|some_viewmode',
    ),
  );

  // I *always* forget this one.
  return $fields;
}



function somemodule_somefield($field) {
  // Store reference to entity (usually a node).
  $entity = $field['entity'];
  // Setup some holder arrays.
  $output = array();
  $content = array();
  $field1 = array();
  // Get an array of all values for the "telefoon" field.
  $field1 = field_get_items($field['entity_type'], $entity, 'field_telefoon');
  // Loop over the values
  foreach ($field1 as $delta => $tel) {
    // Safety because PHP is stupid.
    if (isset($tel['value'])) {
      // create simplest renderable array and stick it in our holder array.
      $output[$delta] = array('#markup' => '<span class="telefoon">' . $tel['value'] . '</span>');
    }
  }
  // Render our holder array and store in content delta 1.
  $content[0] = render($output);
  // Reset holder array.
  $output = array();
  $field2 = array();
  // Get an array of all values for the "email" field.
  $field2 = field_get_items($field['entity_type'], $entity, 'field_email');
  // Loop-di-doop.
  foreach ($field2 as $delta => $email) {
    if (isset($email['value'])) {
      // Same simple renderable array.
      $output[$delta] = array('#markup' => '<span class="mail">' . $email['value'] . '</span>');
    }
  }
  // Put second field in content delta 2.
  $content[1] = array('#markup' => render($output));
  // Render the whole content and return the markups.
  return render($content);
}