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While working on this Unthemely puzzle, I started thinking about traditional crossword specifications and the rationale behind them. Some specs serve a practical purpose. Checking all letters in a grid, for example, reduces the chances of a solver getting stuck on a single unknown answer. Some specs reflect the standards used in adjacent journalistic and entertainment practices. The rules about obscure and indelicate vocabulary fall in this category. Some specs are simply aesthetic choices invented for the medium. The rotational symmetry of black squares is such a choice.
Rather than putting crosswords rules in specific categories, suppose we rank them on a “rationale” scale of 0 to 10, where 0 represents practical/derivative and 10 represents arbitrary. The “No two-letter words” rule might rank a 3 on this scale, while “No more than 72 entries in a themeless grid” might be an 8 or 9. I have a question based on this hypothetical scale: where would you rank the rule that discourages or prohibits the duplication of words or word forms (e.g. EATS and ATECROW) in the same grid? Remember that a ranking reflects how much the rule serves a practical purpose or represents an artistic standard that extends outside the world of crossword puzzles.