We’ve added a new layer type in the Elements panel called Placeholder layers. These layers are designed to be used with the Replace media function we added a few weeks back, and are the perfect way to rough in your projects, templates, or layouts until you’re ready to swap in your final video or file.
Like any other layer type, Placeholder layers have customizable properties, including access to opacity, borders, and animations from the Layers panel. It also includes one special property exclusive to the Placeholder layer type:
Placeholder notes
, where you can leave yourself a reminder about what this layer is going to be. 
When you’re ready to swap in your final content, just select the Placeholder layer and click Add media or select Replace media from the right-click menu.