Hello, I'm trying to understand the different strategies but this one has no documentation. Can someone give a brief explanation of what this strategy consists of?

Original killer sudoku:

https://www.sudokuwiki.org/killersudoku.htm?bd=121221121121334421244441221222121334333124444222121224233331331121224431121331131,0808100700130024130000001700060000001924000000040000000000001815001300261600000000000000001900000000061300000026000
00000140019080807120017000000000000030012000000

Using only strategies 7 and 15 the solver produces:

https://www.sudokuwiki.org/killersudoku.htm?bd=121221121121334421244441221222121334333124444222121224233331331121224431121331131,080810070013002413000000170006000000192400000004000000000000181500130026160000000000000000190000000006130000002600000000140019080807120017000000000000030012000000

The solver cannot proceed further even with all strategies enabled.

Consider the cage starting at d5 and the 1-cell pseudo-cage b5; the cage at d5 cannot be 189 because that would leave b5 empty. Solution is straightforward if the 1's are removed from cage d5.

Here is another board which thwarts the solver.

There is a Killer Sudoku board I would like you to look at

Click on this link:
http://www.sudokuwiki.org/killersudoku.htm?bd=112212212223313412112213413113313443124412241322313311312312211212313322214412211,060012004508000812090009000015270000240017000000000013000003000000000000002706000013000022140000170006000000001600000013000000080000000009001300000012000009001200

The solver fails but the puzzle is easily solved using cage comparison.

The 12-in-2 cage at ab9 must be 9,3 or 8,4. Thus the 8-in-3 cage at abc8 cannot be 1,3,4; it must be 1,2,5 and the solution is straightforward

There is a Killer Sudoku board I would like you to look at

Click on this link:
http://www.sudokuwiki.org/killersudoku.htm?bd=112212211231111123233444223133121221122121331212121312212312312414312414444414444,080015002507001300062300000000002014000000190000000000080000151317000011002200000000200000131700000000001703000000091609000000270000000000380000000000000000000000

The solver fails on this board. It can be easily solved using what I think is an application of cage comparison. The 13-in-2 cage at a78 cannot contain 6,7 because of the 15-in-2 cage at a34. Thus the 5 cell innie in box 3 summing to 45-13-14=18 must contain a 7, 18-in-5 is 12357.

Below is a board that thwarts the solver.

There is a Killer Sudoku board I would like you to look at

Click on this link:
http://www.sudokuwiki.org/killersudoku.htm?bd=112212211213313312244212442114232411112131211232121232231121132132232231111333111,190009001808001700100006000012000005001500070006220000200000001100002100000015270018070000051100000600001814000000000000000000190009002511000014000000000000000000

The solution is straightforward when one notes the hidden pair 1,4 in 5hj and 5fg which leads to a hidden pair 8,9 in 5abc and 6b. I think think this observation would be a result of what I think of as cage comparison.

I am looking forward to the cage comparison documentation. I assume it covers such things as 5 in 2 and 6 in 2 in the same unit, seems very powerful.

If I'm understanding correctly, this strategy is the exact same as Killer Combinations (hard).

Also, the X-Wing strategies and those below it are useless (or at least really rare). Same for KenKen and KenDoku.