There is a built-in clipboard in MailDeveloper for copying and pasting elements around emails.
To copy an element to the clipboard, click the Copy to clipboard -icon in the Tree-view.
When an element is copied to the clipboard, it can be cloned anywhere by dragging the Clipboard-button from the top of the Tree-view.
The clipboard contents are stored in the browser memory, so they work across page changes and even tabs. You can keep two tabs open and copy elements from one tab to another.