When you are working with Designer to edit form you may see the following warning in the report palette:
"Bad value '#f1' of the 'use' attribute of 'font' element - Default will be used."
You may see this error if you delete the “Referenced Objects” node in the Designer hierarchy.
Referenced Objects refer to any repeating objects in the form, fonts, images etc… You can define an object and its properties in the <proto> node in the XML and then just call it many times using its ID through the “use” attribute.
If you delete the Referenced Objects object, the <proto> tag will be deleted, and so the object definitions along with it. The “use” attributes will not be mapped to any object definition and so will result in this warning.
Refer to the XFA 2.4 specification, where, on page 194 it describes how to define these objects in the proto node.