XML :: LibXML：doc - root

Question

这里第一个例子中documentElemtent的调用是多余的吗？

#!/usr/bin/env perl
use warnings;
use strict;
use XML::LibXML;

---

my $file = 'xml_file';

my $doc = XML::LibXML->load_xml( location => $file );
my $root = $doc->documentElement();
my $xpc = XML::LibXML::XPathContext->new( $root );
# ...
say $_->nodeName for $xpc->findnodes( '/' );

输出

#document

---

$doc = XML::LibXML->load_xml( location => $file );
$xpc = XML::LibXML::XPathContext->new( $doc );
# ...
say $_->nodeName for $xpc->findnodes( '/' );

产出也

#document

Answer 1

xpc采用主题节点中定义的任何前缀，因此如果在根节点上定义了前缀，则两者是不同的。

use warnings;
use strict;
use feature qw( say );

use XML::LibXML qw( );

my $xml = <<'__EOI__';
<root xmlns:foo="uri:xxx">
<foo:bar/>
</root>
__EOI__

my $doc  = XML::LibXML->load_xml( string => $xml );
my $root = $doc->documentElement();

{
   my $xpc = XML::LibXML::XPathContext->new($doc);
   say "doc:";
   say $_->nodeName for $xpc->findnodes('foo:bar');
}

say "";

{
   my $xpc  = XML::LibXML::XPathContext->new($root);
   say "root:";
   say $_->nodeName for $xpc->findnodes('foo:bar');
}

doc:

root:
foo:bar