How do I set the contents of the "message" element?

I am working on a customized Joomla template and I would like to assign a value to the "message" type element. I've set it in the past but have struggled for the past 2 days to find how i assigned a value to this element. Any help would be hugely appreciated?

The element that I am talking about is described in the jdoc statement

<jdoc:include type="message" />
This element should only appear once in the <body> element of the Template to render system and error messages that occurred in the request.

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Resolved How do I set the contents of the "message" element?