This pipeline, used in ecrire/inc/rechercher.php, is used to declare the searches that should be executed on other tables rather than the table explicitly referenced in a loop.
For example, a search for an author name for an ARTICLES loop returns the articles that this author has written (by searching in the spip_auteurs_articles
table).
This pipeline receives an array of tables containing an array of table, field, weighting triplets (like the pipeline "rechercher_liste_des_champs").