The parentheses in regular expressions define so called "capture groups". Originally, you had two capture groups: 
m/<tagid=(\d*)([[:alpha:]]*)>/
         <~~~><~~~~~~~~~~~~>
          #1        #2

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The variables $1 and $2 contain the parts matched by the respective capture groups. \d* means "zero or more digits", [[:alpha:]]* means "zero or more characters". In your new regex, you don't have any parentheses: 
m/<endnote id=/

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So $1 and $2 aren't populated.

map{substr$_->[0],$_->[1]||0,1}[\*||{},3],[[]],[ref qr-1,-,-1],[{}],[sub{}^*ARGV,3]

In reply to Re^3: read/write delete duplicates/sort PROBLEM! - Use of uninitialized value in sprintf by choroba
in thread read/write delete duplicates/sort PROBLEM! - Use of uninitialized value in sprintf by VladP

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