Reading subimage-search command line results

[kraftydevil]

compare -metric RMSE -subimage-search writes a value with format 'A (B) @ X,Y' to stderr.

Examples:

1. 0 (0) @ 94,86
2. 15903.7 (0.242675) @ 233,304
3. 22620 (0.34516) @ 614,126

So far I'm pretty sure of these values:
B = similarity threshold of match
X = x-coordinate of match
Y = y-coordinate of match

Question 1
What is A for? It's obviously 0 when there's a match, so I'm sure A and B are related - I just can't tell the relationship.

Question 2
Can the return format ever be different? For example, is there a way to get a list of the top 3 matches?

[fmw42]

A is the score in the quantum range of your ImageMagick compile (default for Q16 is 0 to 65535). B is in the range 0 to 1