In the first example, the name of selected Use Case Diagrams in the project will be output. Note that "Use Case Diagrams (Admin)" is the field name, which is a required and unique value for identifying this field.
In the second example, the image of selected diagrams in the project will be output.
In the third example, content will be output for each of the selected diagrams in the project, based on the template MyTemplate.
When you pick-up a Doc Base with such a ${DIAGRAM} field in it, you can select the diagrams to query in Doc. Composer.