EDIT

/**

 * Returns HTML for annotations to cdm objects.

 *

 * Almost any cdmObject may be annotated. Therefore we provide a generic way to

 * display as well as create or update annotations. The following cdm classes

 * are annotatable:

 *

 * - DescriptionElementBase

 * - EventBase

 * - HomotypicalGroup

 * - IdentifiableEntity

 * - DescriptionBase

 * - IdentifiableMediaEntity

 * - Media

 * - Sequence

 * - TaxonBase

 * - TaxonName

 * - TaxonomicTree

 * - TermBase

 * - LanguageStringBase

 * - ReferencedEntityBase

 * - NomenclaturalStatus

 * - OriginalSourceBase

 * - RelationshipBase

 * - TypeDesignationBase

 * - TaxonNode

 * - WorkingSet

 *

 * @param array $cdm_entities

 *   An array of CdmBase instances.

 * @param $footnote_list_key_suggestion string

 *    optional parameter. If this parameter is left empty (null, 0, "") the

 *   footnote key will be determined be set to

 *   RenderHints::getFootnoteListKey().FOOTNOTE_KEY_SUFFIX_ANNOTATIONS otherwise the supplied

 *   key will be used.

 *

 * @return string

 *   The markup.

 */

function cdm_entities_annotations_as_footnotekeys($cdm_entities, $footnote_list_key =null){

  // check if footnotes for annotations are disabled completely

  if (variable_get('cdm_dataportal_annotations_footnotes', CDM_DATAPORTAL_ALL_FOOTNOTES)) {

    return '';

  }

  $out = '';

  if(is_array($cdm_entities)){

    // array of entities

    $footNoteKeys = cdm_entities_annotations_footnote_keys($cdm_entities, $footnote_list_key);

  } else {

    // single entity

    $footNoteKeys = cdm_entity_annotations_as_footnote_keys($cdm_entities, $footnote_list_key);

  }

  foreach ($footNoteKeys as $a) {

    $out .= cdm_footnote_key($a, ($out ? ',' : ''));

  }

  return $out;

}