+If you tick the \q{X} checkbox, Solo will apply the optional extra
+constraint that the two main diagonals of the grid also contain one
+of every digit. (This is sometimes known as \q{Sudoku-X} in
+newspapers.) In this mode, the squares on the two main diagonals
+will be shaded slightly so that you know it's enabled.
+
+If you tick the \q{Jigsaw} checkbox, Solo will generate randomly
+shaped sub-blocks. In this mode, the actual grid size will be taken
+to be the product of the numbers entered in the \q{Columns} and
+\q{Rows} boxes. There is no reason why you have to enter a number
+greater than 1 in both boxes; Jigsaw mode has no constraint on the
+grid size, and it can even be a prime number if you feel like it.
+
+If you tick the \q{Killer} checkbox, Solo will generate a set of
+of cages, which are randomly shaped and drawn in an outline of a
+different colour. Each of these regions contains a smaller clue
+which shows the digit sum of all the squares in this region.
+