Function VirtualKeyboardLayer

Remarks

A virtual keyboard belongs to the focused text field, and the grid surface is not one. Each pane's layer hosts an input and registers it as the pane's focus target while in keyboard mode, asking for the keyboard's input mode. Keys typed there reach the SheetCellEditorStartLayer as keys aimed at the surface do; this layer starts no edits of its own.

Per pane:

• A tap on the grid leaves keyboard mode: the user has gone back to touching cells. With the store's keepOnTap it stays, as Excel keeps its keyboard: the tap does not move focus off the input.
• A focus that reaches the surface itself in keyboard mode is passed on to the input.
• Leaving keyboard mode with the input focused hands focus to the surface, lowering the keyboard.

The primary pane's layer (the center pane, when there is one) also does the sheet's part, once:

• On and off with the keyboard. A keyboard rising while the sheet is being edited (in the cell or a formula bar) enters keyboard mode; the keyboard going down (the system's back gesture, its own hide key) leaves it.
• Show. Entering keyboard mode with focus outside any text field (a "show keyboard" button) focuses the pane, raising the keyboard.
• Done. Taking a way out of the edit from chrome (the status bar's ✓ / ✕, see exitEditMode) leaves keyboard mode before the edit ends, so the focus returning to the grid lowers it.
• The active cell stays in view. When the keyboard takes room from the grid, or a KeyboardAccessory (the formula bar riding the keyboard) settles over the active cell, the cell is scrolled back into view (unless the store's disableScrollIntoView).

Mount it directly above the start layer, so a key typed into the input reaches the start layer's floor. It renders nothing where the keyboard store is not enabled (isEnabled(): a device with no virtual keyboard).