Fragmentainer

A fragmentainer is defined in the CSS Fragmentation specification as follows:

A box—such as a page box, column box, or region—that contains a portion (or all) of a fragmented flow. Fragmentainers can be pre-defined or generated as needed. When breakable content would overflow a fragmentainer in the block dimension, it breaks into the next container in its fragmentation context instead.

Fragmented contexts are found in CSS paged media, where the fragmentainer would be the box that defines a page. In CSS multiple-column layout, the fragmentainer is the column box created when columns are defined on a multicol container.