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In Jira Specifications tab, we have different project where we mentioned or write down the feature. But as of now linking issues in cross project is not possible. Do anyone knows how to do it?
What do you mean by linking and specifications tab?
I ask because when you say linking, most Jira people would look at "issue links", where you can link any issue to any other (as long as you can see the issues in the other projects). So I'm not sure if that's what you mean because that function absolutely does do cross-project.
Plain Jira does not have a "specifications tab" so we'll need you to explain that a bit more before we can help you with it.