The bugzilla product kwin has several Components. Here a short overview is peresented.
Component general for untriaged bugs or not fitting anywhere else.
Core components include everything that is part of KWin core.
Bugs directly in the core of KWin. E.g. stacking order related
Everything related to Alt+Tab except effects
Everything related to window tiling.
Everything related to client grouping aka window tabbing. This is the crashers in core, but not the implementation in decorations.
Multi screen related bugs
As before everything to multi head (two+ X servers)
Bugs related to XRandR (modern). General multiscreen issues should be put into this component.
Anything to Xinerama/Twinview (legacy).
Compositing related bugs in the core (not effects).
General bugs either in the effects library or it's implementation in core and scene.
OpenGL related compositor bugs.
Xrender related compositor bugs.
Bugs in the decoration libraries (KDecoration and KCommonDecoration) plus bugs in the bridge.
Bugs in various decorations shipped with KWin (e.g. Plastik), but not Oxygen (has own component and product) and not Aurorae.
Bugs in the Aurorae Theme Engine
Bugs in any effects not matching into the more specialized components.
Bugs in any tabbox related effects (boxswitch, coverswitch, flipswitch).
Bugs in effects for window management (e.g. PresentWindows and desktop Grid).
Removed component eyecandy: should be merged into effects-various.