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Queries are an internal means to communicate about a specific document. Whatever the module you are in, you will always have the ability to create and post a query related to this object. This query is then submitted to the other staff members and will appear in their worklists as a pending query that needs an answer.
Target the document you want to ask a question about
Follow the discussion in the query module or on the related document directly thank to the "Jump to queries" link
Close a query when it has been answered, and the entire thread will be archived but yet accessible