If the tag’s output is not a numeric type, it will be considered as being 0 (zero) and the filter will simply return its own argument:[(#TEXTE|plus{18})] will return "18".
It is possible to assign a negative number as the argument to the filter:[(#TOTAL_BOUCLE|plus{-5.2})], but this would undoubtedly be more clear if we were instead to use the |moins (subtract) filter.
Warning: if xx is a floating point number, it must be written with a period as per the English method as opposed to being written with a comma as some European languages do:[(#TOTAL_BOUCLE|plus{5.2})].
See also
Other mathematical operation filters