It appears to be looking for and capturing lines containing page numbers in one of 4 forms. Roughly: 

'      nnn   <page>   '
'    - nnn - <page>   '
'      A-nnn <page>   '
'  page nnn of mmm    '

[download]

This becomes fairly clear if you break up and expand the regex a little using /x. 

my $pattern = qr[
    (
            \n\s*   [0-9]{1,3}          \s*\n\s* <page>       \s*\n
        |    
            \n\s* - [0-9]{1,3} -        \s*\n\s* <page>       \s*\n
        |
            \n\s*   [A-Za-z]-[0-9]{1,3} \s*\n\s* <page>       \s*\n
        |
            \n\s*  page \s* [0-9]{1,3}  \s* of \s* [0-9]{1,3}  \s*\n
    )
]x;

[download]

There are many ways the regex could be improved, but that isn't what you asked :)

Examine what is said, not who speaks.        The end of an era!
"But you should never overestimate the ingenuity of the sceptics to come up with a counter-argument." -Myles Allen
"Think for yourself!" - Abigail        "Time is a poor substitute for thought"--theorbtwo         "Efficiency is intelligent laziness." -David Dunham
"Memory, processor, disk in that order on the hardware side. Algorithm, algorithm, algorithm on the code side." - tachyon

In reply to Re: what the pattern searches for by BrowserUk
in thread what the pattern searches for by agynr

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