[ ] Allow default values for onePoint layers. Required for Sudoku pencil marks, and helpful for CellOutlineLayer.
[ ] Layers to add
[ ] Sudoku
[ ] SudokuPencilMarks
[ ] SudokuArrowSums
[ ] KillerCages
[ ] SimpleLine
[ ] MultiPointLine
[ ] Show a list of active layers and allow activating and deactivating them
[ ] Keep the SelectionLayer and CellOutlineLayer hidden unless explicitly requested
[ ] Allow to tab through layers and have controls drop through to the next layer
[ ] How should Pseudo-layers work? I want something that can combine parts of existing layers into one layer. This will not be the same thing as a Preset. Or will it?
[ ] Perhaps pseudo-layers should have some of the capabilities of the SelectionLayer. In other words, the SelectionLayer could be implemented as a pseudo-layer; whatever that entails.
CellOutlineLayer
.