The Content Block component designates regions on the page where
pre-styled instances can be inserted in
Content mode.
In Content mode, you can edit any direct child instances that were
pre-added to the Content Block, as well as add new instances predefined
in Templates.
To predefine instances for insertion in Content mode, switch to Design
mode and add them to the Templates container.
To insert predefined instances in Content mode, click the + button while
hovering over the Content Block on the canvas and choose an instance
from the list.