__DATA__
<open> tag 1 <close> 
notatag 1
<open> tag 2 <close>
notatag 2
<open> tag 3 a <open> tag 3 b <close> tag 3 c <close>
notatag 3
<open> 
    tag 4 a 
    <open> tag 4 b <close> 
    <open> 
        tag 4 c 
        <open> tag 4 d <close>
        tag 4 e 
    <close> tag 4 f
<close>
notatag 4