Sorry, no image uploads on the Archibus forums, so I'm cross-posting here.
In order to add a hover-over tooltip (or click to open a dialog box with the same message), use the Tooltip tags. In order to display an always-visible line of text in conjunction with a field, use Instructions tags.
The attached screenshot shows both.Code:<tooltip> The data in this fields needs to include X. </tooltip> <instructions>Please be detailed when reporting Y data.</instructions>