Use a tabular layout for slices .
A slice-to-slice assignment like:
@frames[-1,-2,-3] = @active{'top', 'prev', 'backup'};
can also be written as:
@frames[ -1, -2, -3 ] = @active{'top', 'prev', 'backup'};
This second version makes it immediately apparent which hash entry is being assigned to which array element. Unfortunately, this approach is useful only when the number of keys/indices in the slices is small. As soon as either list exceeds a single line, the readability of the resulting code is made much worse by vertical alignments:
@frames[ -1, -2, -3, -4, -5, -6,
-7, -8 ]
= @active{'top', 'prev', 'backup', 'emergency', 'spare', 'rainy day',
'alternate', 'default'};