my $str = 
  q[<APPEND changed_date="02-02-2003">This is sample text</APPEND>];

print "match: ", $str =~ m{ <APPEND (.*?) > }x, $/;
print "post:  ", $', $/;

__output__

match:  changed_date="02-02-2003"
post:  This is sample text</APPEND>