Crosswords are one of those interesting things where there is a quite a bit of trans-atlantic difference which is worth taking a brief look at if you aren't familar. To quote Wikipedia:
> Crossword grids such as those appearing in most North American newspapers and magazines consist mainly of solid regions of uninterrupted white squares, separated more sparsely by shaded squares. Every letter is "checked" (i.e. is part of both an "across" word and a "down" word) and usually each answer must contain at least three letters. In such puzzles shaded squares are typically limited to about one-sixth of the total. Crossword grids elsewhere, ... have a lattice-like structure, with a higher percentage of shaded squares (around 25%), leaving about half the letters in an answer unchecked.