G'day Sarah,

There's nothing wrong with either assertion. The apparent problem occurs because the first '.*' matches 'cat' and all the whitespace that follows it but nothing matches 'bird' and all the whitespace that precedes it.

Here's a simplified example of what you're currently doing:

$ perl -E 'say("X\n\t99\n\tY" =~ /(?<=X).*\d+(?=Y)/s ? 1 : 0)'
0
[download]

Here's how you might fix that:

$ perl -E 'say("X\n\t99\n\tY" =~ /(?<=X).*\d+.*(?=Y)/s ? 1 : 0)'
1
[download]

I'd also suggest you take a look at "perlre: Modifiers": note I only used 's'; the 'gxi' are not needed.