I have assigned the familiy names of plant pictures in Undercategories and the species names in Tags. After having saved the Meta-Data in the files, the order of the saved contents of the Undercategories and species, respectively is random:
Either the Undercategoriy is the first entry in the ITPC-field, or the Tag:
(1) not correct: Undercategory: Orchidaceae
Tag: Aceras anthropophorum
ITPC: Aceras anthropophorum;Orchidaceae
Tag: Heracleum sphondylium
ITPC: Apiaceae; Heracleum sphondylium
I would like always to have in the first place the name of the Undercategory followed by the name of the Tag (of course, the Tag belongs to the respective Undercategory).
I don't see how Elements (or any other managing software) could manage the order of IPTC items. IPTC data is not stored at all in the catalog, it's only read from the data stored in the metadata header of the file (or in the xmp sidecar file). You can manage keywords in hierarchies with a catalog, but the way IPTC keywords are stored is not hierarchically and probably depends more on your OS and OS version than on the input and display order from an external photo editor. I would have expected a display either in random or alphabetical order.