X-Wing operates on two rows (or columns) aligned with two columns (or rows).   Can it be extended to three rows and columns?  Logically yes, and we’re taking about a grid of nine cells here, not four, but interestingly not everyone of the nine cells needs to have the number under consideration. 

Let’s look at the Sword-Fish ‘grid’ and see what’s going on. Here we are looking at all the 5 candidates in this Sudoku, everything else removed.

Three rows all have three number 5’s on them: rows B, F and G.  It so happens that all the fives are aligned vertically on the same columns (2, 5 and 8).  The intersection of these three rows and columns occurs at nine points (circled) but only three of these cells can be a 5 and still confirm to Sudoku rules.   We don’t know which three of the nine (apart from B5 which has been eliminated earlier).  But they are all locked and mutually exclusive.   Because of this there can be no 5’s along the lines of this grid.   All 5’s in the grey columns in this example can be removed.

If we reveal the actual Sudoku you’ll agree it’s pretty hard to see and it will be a diabolical grade if this strategy is necessary.