I am currently undertaking the ACP-100 exam prep course.
In the 1. Module Advanced User Features - "sample exam questions" I get asked the following question.
Inspect the JQL query shown below.
category = "Mobile App" AND project = Customer1 AND created >= startOfWeek(-1) OR project + Customer2 AND created > startOfWeek(-1)
project + Customer2
I couldn't find anything about it in the offical documentation that the + operator is supported
https://support.atlassian.com/jira-software-cloud/docs/jql-fields/
I also tested this in my lab instance.
So could this be a typo?