Spacers fill unused space along the parent’s axis and are used to lay out other content. If there are multiple spacers or other elements whose size along the parent’s axis is set to fill, they’ll split the unused space evenly.
Spacers are different than other elements in Play because they don’t have any properties of their own. They don’t have any styles or interactions, and they inherit their size from their parent and siblings. They can, however, be hidden.