What could be the Isssue?

Not enough manual reading/understanding 

$ perl -MHTML::Tree -e " print HTML::Tree->new_from_content(q{<header>
+<article>})->as_HTML"
<html><head></head><body></body></html>

$ perl -MHTML::Tree -le " print HTML::Tree->new(qw{ ignore_unknown 0 }
+)->parse_content(q{<header><article>})->as_HTML"
<html><head></head><body></body><header><article></article></header></
+html>

$ perl -MHTML::HTML5::Parser -le " print HTML::HTML5::Parser->load_htm
+l( string => \q{<header><article>}) "
<?xml version="1.0" encoding="utf-8"?>
<html xmlns="http://www.w3.org/1999/xhtml"><head/><body><header><artic
+le/></header></body></html>

$ perl -MMojo::DOM -le " print Mojo::DOM->new( q{<header><article>} ) 
+"
<header><article></article></header>

[download]
$ perl -MXML::LibXML -le " print XML::LibXML->new( qw/ recover 2 / )->load_html( string => q{<header><article>} ); " <?xml version="1.0" standalone="yes"?> <!DOCTYPE html PUBLIC "-//W3C//DTD HTML 4.0 Transitional//EN" "http://www.w3.org/TR/REC-html40/loose.dtd"> <html><body><header><article/></header></body></html> </c>

htmltreexpather.pl , Parsing HTML / Re^4: Parsing HTML, A regex question , NASA's Astronomy Picture of the Day / Re: NASA's Astronomy Picture of the Day , Re: Extracting HTML content between the h tags, Re^2: Help With Online Table Scraper, Re^4: web::scraper using an xpath, .... HTML Parser suggestions, Extract Portion of HTML

In reply to Re: HTML::Treebuilder look_down not working with <header>, <article> etc by Anonymous Monk
in thread HTML::Treebuilder look_down not working with <header>, <article> etc by Anonymous Monk

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