ref: 3a3e491a8bc624eb1c3b34e54ebee8d33942add2
dir: /html/filling.html/
Filling <p> Write a number in every blank square of the grid. When the grid is full, every orthogonally connected group of identical numbers should have an area equal to that number: so 1s always appear alone, 2s in pairs, and so on. <p> To place a number, click the mouse in a blank square to select it, then type the number you want on the keyboard. You can also drag to select multiple squares, and then type a number to place it in all of them. To erase numbers, select one or more squares in the same way and then press Backspace.