Editing Chess960 (section)

===Observations===
* In some starting positions, squares can remain occupied during castling that would be required to be vacant under standard rules. Castling a-side (0-0-0) could still be possible despite the home rank a-, b-, or e-file squares being occupied, and similarly for the e- and h-files for h-side castling (0-0). In other positions, it can happen that one of the king or rook does not move during the castling maneuver since it already occupies its destination square – e.g., an h-side rook that starts on the f-file; in this case, only the king moves. No initial position allows a castling where neither piece moves, as the king must start between the rooks.
* Another unusual possibility is for castling to be available as the first move of the game, as happened in the 11th game of the tournament match between [[Hikaru Nakamura]] and [[Magnus Carlsen]], Fischer Random Blitz 2018. The starting position had kings at f1/f8 and h-side rooks at g1/g8. Both players took the opportunity to castle on the first move (1.0-0 0-0).<ref>{{cite web |url=https://en.chessbase.com/post/chess960-day-5 |title=Carlsen adds a new title: Chess960 champion |publisher=[[ChessBase]] |date=February 14, 2018 }}</ref>
* In standard chess, a rook can castle out of and through a threatened square but cannot castle into a threatened square. While there are no rules specifying that a rook cannot castle into a threatened square, they are naturally unable to. This is because a castling king will pass through the square the castling rook ends up on and the rules prohibit a king to pass through threatened squares during castling. In Chess960, however, the relative position of the King and Rooks sometimes allows for a rook to legally end up on a threatened square. This is discussed by [[Levon Aronian]] and [[Yasser Seirawan]] in Round 3 of St Louis' 2022 Chess 9LX tournament for move 18 of Aronian's game against [[Leinier Domínguez Pérez]] which had starting position RKBBNQNR.<ref>{{citation |url=https://www.youtube.com/watch?v=p2CjJa78c24 |title=Aronian: Beating Kasparov Day 1 |website=[[YouTube]] |date=September 14, 2022 }}</ref><ref>{{citation |url=https://www.youtube.com/watch?v=LIwinEQ9KFQ |title=Levon mansplains 9LX castling to Yasser. (2022Sep) |website=[[YouTube]] |date=November 11, 2022 }}</ref><ref>{{citation |url=https://lichess.org/broadcast/2022-champions-showdown-chess-9lx/round-3/RKKa66zy/L8FqHntz#35 |title=2022 Champions Showdown: Chess 9LX Round 3: Aronian, Levon - Dominguez, Leinier |website=[[Lichess]] |date=September 14, 2022 }}</ref>
* There are exactly 90 starting positions where, unlike in standard chess, players have to give up castling rights on one side in order to castle on the other side. This is seen by calculating that this happens 18 times in each of five possible groups of starting positions namely RKRXXXXX, RKXRXXXX, XRKRXXXX, XXXXXRKR and RXKRXXXX. In only these positions, a rook has to be moved (or captured) on one side in order to castle on the other side.<ref name="chess.stackexchange.com">{{Cite web|url=https://chess.stackexchange.com/questions/37082/how-many-chess960-positions-exist-in-which-castling-on-one-side-does-not-require|title = Chess Stackexchange – How many Chess960 positions exist in which castling on one side does not require moving the rook on the other side?}}</ref> For example, in the starting position RKRBBNNQ, which is in the first group RKRXXXXX, a player intending to castle a-side must first move the c-file rook (or let it be captured).
** The Sesse evaluations<ref name="Sesse 1">{{Cite web|url=https://www.chess.com/article/view/whats-the-most-unbalanced-chess960-position|title=What's The Most Unbalanced Chess960 Position?|first=Mike|last=Klein (MikeKlein)|website=Chess.com|date=March 14, 2018 }}</ref><ref name="Sesse 2">{{Cite web|url=https://docs.google.com/spreadsheets/d/1JVT6_ROOlCTtMmazzBe0lhcGv54rB6JCq67QOhaRp6U/edit#gid=0|title = Fischer Random – 960 startposisjoner}}</ref> (which used [[Stockfish (chess)|Stockfish 9]]) show that White has about, on average, a 7% increased advantage in these 90 positions (Evaluation is 0.1913) compared to the remaining 870 positions (Evaluation is 0.1790).<ref name="ReferenceA">{{Cite web|url=https://chess.stackexchange.com/questions/38722/what-is-whites-increased-advantage-in-chess90-as-compared-to-chess870-chess96|title = Chess Stackexchange – What is white's increased advantage in chess90 as compared to chess870? (Chess960 can be split into 2 subsets, chess90 and chess870)}}</ref>