{branche} selects all the articles in the section AND its sub-sections.
This is a kind of extension of the {id_secteur} criteria.
Searches for the item identifier in the first parameter of the criterion {branche XX}if it is filled in, otherwise, without parameter ({branche} in the parent loops. It is used to calculate the list of field identifiers for the entire branch.
The loop that has this criterion looks for a possible link with the column heading_id, and will try to find a join with another table if it is necessary to obtain it.
This criterion should be used with caution: if your site is well structured, you should not need it, except in very special cases.