Reuse Elements from Warehouse Topics
You can reuse content with content references (conref) by copying and pasting elements, dragging and dropping elements, or by using the Content Editor toolbar.
Per DITA standard, some elements can only be used in a topic once. For example, shortdesc, prereq, result, postreq. If you're trying to reuse such an element, first remove it from your topic, then reuse the element. In the case of shortdesc, you can wrap it in abstract instead, which can contain multiple shortdesc elements.
Reuse elements by using the Content Editor toolbar
You reused an element from a warehouse topic with the content reference (conref) mechanism. In the Content Editor, reused content has gray background. When you click it, you see options to open the warehouse topic (Open), point the conref to a different element (Change), edit reused content in the warehouse topic (Edit Content), and remove the conref (Remove).