Backdrop --> Backdrop Layer, 706 Background pen, 584 BACKGROUNDPEN, 58, 141 Backup - of display areas, 705 Beam synchronization, 600 BeginIO(), 448, 449, 520, 886 BeginRefresh(), 95, 97, 97, 110, 115, 128, 244, 261, 721 BeginUpdate(), 128, 711, 721 Behind - open screen, 49 BehindLayer(), 708, 711 Bell - visible, 75 BgPen - in RastPort, 584 BindDrivers, 758 BitMap --> BitMap Structure --> BitMapScale(), 598, 612 BitPlane --> BLIT Interrupts, 519 Blitter --> Block - graphics with layers, 708 Block Input, 203 Block Pen, 106 BLOCKPEN, 57 BltBitMap(), 596, 597, 612 BltBitMapRastPort(), 596, 597, 612 BltClear(), 592, 612 BltMaskBitMapRastPort(), 596, 598, 612 bltnode structure, 600 - creating, 601, linking blitter requests, 600 BltPattern(), 594, 612 BltTemplate(), 595, 596, 612 BNDRYOFF(), 590, 611 Bob structure, 635 Bobs - introduction, 613, simple definition, 615 BoolInfo structure, 139 BOOLMASK, 139 Boopsi --> Border --> Border structure --> BORDERHIT, 648 Borderless --> bottommost - in GelsInfo, 624 Box - menu item, 180 Break key, 432 Broadcast - IDCMP events, 248 BuildEasyRequest(), 217, 218-219, 222 BuildEasyRequestArgs(), 219, 222 BuildSysRequest(), 218, 222 Bus error, 474 BUserStuff, 651 Busy Pointer, 274 buttongclass, 297 buttonglclass, 315 B-Pen - see BgPen