The Diagram's AI implements rules of not passing through or out of check as a generalized en-passant capture, where in the case of a royal any piece would be allowed to make the capture through its normal capture moves. So whether moving through check is allowed can be indicated in the move of the royal by having it create e.p. rights. For castling this is implied already by the O atom, also that the starting square itself becomes an e.p. square, so that castling out of check is also illegal.

XBetza uses the n on a stepper atom (W, F, where non-jumping has no meaning) to indicate it creates rights. On sliders that repeat such steps I now create them only at the end-point of each step. So that nQ on a royal means you cannot move through check, but you can move out of check. Which is in general what you want. That you also create rights where the piece ends up doesn't matter, as the piece could be captured there anyway. If it would automatically also create rights on the starting square of a slider leg, it would be rather cumbersome to describe the case where you want to allow moving out of check; you would have to make it a 2-leg move, first making a single step without creating rights, and then continue as a slider (through a range toggle), a sort of 'rectified' Griffon, yafnK. So I opted for creation of rights at the target square of a step, also for single steps.

But for Apothecary Chess you want to have this on larger leaps, where the n cannot be used for this purpose, and you want it on the initial square. The solution is very cumbersome: you would have to break up the N and C moves into King steps seamlessly glued through mp modes, and furthermore make an extra back-and-forth step to the starting square to make the step that arrives there create the e.p. rights, as a step that leaves it can not.

Perhaps I should just adopt the convention that initial moves on royal pieces automatically create the rights at the starting square, so that they can never be made out of check. This is usually the rule. The problem is that you can then never indicate that you do want to allow it out of check. Another possibility would be to double the i modifier for this purpose, as an indication you have to be 'extra virgin' to make the move, i.e. not even checked.

[Edit] For now I have disabled all i moves on a royal piece that is in check, in the AI. (It doesn't make a distiction based on the number of i.) I also changed the handling of e.p. capture by the AI somewhat: at any square along its path the piece checks whether it hits a square for which e.p. rights exist. If they do, and the move can capture e.p. has e mode, or c mode when the last moved piece was a royal, it allows the e.p. capture irrespective of the square occupant. For e.p. on non-royals you better make sure they never generate rights on a square occupied by an enemy. For royals, the captures are never really made, but as soon as it is detected they are possible the line terminates with a winning score, as it would mean the royal gets captured. This allows for instance forbidding hopping over enemy pieces that are protected, as is needed in Metamachy.