In RSF, a container is a component of type UIContainer. UIContainer simply has the function of containing other components, in a "free-form" way (as opposed to hardwired component "clusters" such as UISelect). UIContainer can't be used usefully except as a base class - e.g. UIForm and UICommand are derived from UIContainer, via the concrete intermediary UISimpleContainer. The "other" line of descent from UIContainer which avoids UISimpleContainer contains only UIBranchContainer. Note that these classes unlike components from other frameworks are all very small, and specify virtually no behaviour. The "container" hierarchy is probably the most untypical in RSF in that it does actually contain some methods, but just to abstract the functions of locating and iterating over child components.

See the dedicated page on primitive components for more details.