The delimiters matter, so

use YAPE::Regex::Explain;
print YAPE::Regex::Explain->new(
qr{<ID>([^<]+)</ID>}
)->explain;
__END__
The regular expression:

(?-imsx:<ID>([^<]+)</ID>)

matches as follows:
  
NODE                     EXPLANATION
----------------------------------------------------------------------
(?-imsx:                 group, but do not capture (case-sensitive)
                         (with ^ and $ matching normally) (with . not
                         matching \n) (matching whitespace and #
                         normally):
----------------------------------------------------------------------
  <ID>                     '<ID>'
----------------------------------------------------------------------
  (                        group and capture to \1:
----------------------------------------------------------------------
    [^<]+                    any character except: '<' (1 or more
                             times (matching the most amount
                             possible))
----------------------------------------------------------------------
  )                        end of \1
----------------------------------------------------------------------
  </ID>                    '</ID>'
----------------------------------------------------------------------
)                        end of grouping
----------------------------------------------------------------------
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