It really depends how you are wanting to use those. If you are wanting
to use the summary in an email's subject line then you probably want it
to be fairly short for example. You can have as many labels/annotations
as you like, so you don't even have to have one called "summary" if you
don't want to, and there's nothing stopping you from having much more
specific labels (e.g. severity, service, environment) which you can then
include in email/ticket subjects.
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Stuart Clark