for a larger sw architecture, I group my use cases and my requirements into different files. I have a file use_cases.iuml and reqs.iuml. These files contain only the element defintions, no links. I want to create diagrams which show the linking use case to requirement. I use the !include statement for including use_cases.iuml and reqs.iuml. In the file with the linking use case to requirements I now get all use cases and all requirements. It would be fine to hide all unlinked elements in a section.
usecase UC1 as "do something useful"
usecase UC2 as "control state of cpu"
artifact RQ1 [
A requirement text.
artifact RQ2 [
Another requirement text
skinparam packageStyle rectangle
'all other elements are hidden
'only linked are shown in diagram
UC1 -- RQ1
UC1 -- RQ2