The CSS regions module allows content to flow across multiple areas called regions. The regions are not necessarily contiguous in the document order. The CSS regions module provides an advanced content flow mechanism, which can be combined with positioning schemes as defined by other CSS modules such as the Multi-Column Module [CSS3COL] or the Grid Layout Module [CSS3-GRID-LAYOUT] to position the regions where content flows.

Displaying the complex layouts of a typical magazine, newspaper, or textbook on the web requires capabilities beyond those available in existing CSS modules. Dynamic magazine layout in particular requires flexibility in placement of boxes for content flows. This is the purpose of the CSS regions module.

For more complex layouts, content needs to flow from one area of the page to the next without limitation on the areas' sizes and positions. These arbitrary areas are the target of specific content flows which this document calls named flows. Each named flow can be associated with a set of CSS Regions called a region chain. CSS Regions are based on the rectangular geometry of the CSS box model. Content in a named flow is taken out of the normal visual formatting and rendered in a chain of CSS Regions.