[Koha] Classification Confusion

[Roger Buck]

Can anyone please clarify the difference(s) between Koha/Opac "Format",
"Item Type", "Class" and "Group"?

Where the confusion started:
When using "Advanced" search options menu (/catalogue/index.html), I
note the option to search by "Class" but I cannot find a way to add an
Item/Title to a "Class" entry in the Catalogue.

Where I have looked for more clarification:
When viewing the biblio using the  moredetail.pl option, I see a "Group"
option that includes "Class" and "Item Type" options inside the "Group"
sub-menu.

Comparing entries for "Format", "Group" and "Item Type":
When using "normal" Acquisitions method to add a new biblio to basket, I
see an option list for "Format". The "Format" option list includes
select items that appear to include both "Group" and "Item Type" names.

So,

1. Is "Format" the sum of "Group" + "Item" type?

2. Should the search option box be rename to search by "Format" instead
of by "Class"... or none of the above %-|


Any help in clarifying my befuddled brain would be appreciated.

Yours faithfully, "confused" of Sydney.

R.