Constant xcb::xproto::CW_BACKING_STORE

pub const CW_BACKING_STORE: Cw = 0x40;

A backing-store of WhenMapped advises the server that maintaining contents of obscured regions when the window is mapped would be beneficial. A backing-store of Always advises the server that maintaining contents even when the window is unmapped would be beneficial. In this case, the server may generate an exposure event when the window is created. A value of NotUseful advises the server that maintaining contents is unnecessary, although a server may still choose to maintain contents while the window is mapped. Note that if the server maintains contents, then the server should maintain complete contents not just the region within the parent boundaries, even if the window is larger than its parent. While the server maintains contents, exposure events will not normally be generated, but the server may stop maintaining contents at any time.