The rules that use the category "<except>" are:

<unit>

<det-not_other-not_indef-pl> <call_sign_prefix> units <except> <unit-not_except>

<unit-pl>

<det-not_other-not_indef-pl> <call_sign_prefix> units <except> <unit-not_except>

<items>

<item_or_items> <except> <item_or_items>