XML::LibXML Class for Element Nodes
new 	

$node = XML::LibXML::Element->new( $name )

This function creates a new node unbound to any DOM.
setAttribute 	

$node->setAttribute( $aname, $avalue );

This method sets or replaces the node's attribute $aname to the value $avalue
setAttributeNS 	

$node->setAttributeNS( $nsURI, $aname, $avalue );

Namespaceversion of setAttribute.
getAttribute 	

$avalue = $node->getAttribute( $aname );

If $node has an attribute with the name $aname, the value of this attribute will get returned.
getAttributeNS 	

$avalue = $node->setAttributeNS( $nsURI, $aname );

Namespaceversion of getAttribute.
getAttributeNode 	

$attrnode = $node->getAttributeNode( $aname );

Returns the attribute as a node if the attribute exists. If the Attribute does not exists undef will be returned.
getAttributeNodeNS 	

$attrnode = $node->getAttributeNodeNS( $namespaceURI, $aname );

Namespaceversion of getAttributeNode.
removeAttribute 	

$node->removeAttribute( $aname );

The method removes the attribute $aname from the node's attribute list, if the attribute can be found.
removeAttributeNS 	

$node->removeAttributeNS( $nsURI, $aname );

Namespace version of removeAttribute
hasAttribute 	

$boolean = $node->hasAttribute( $aname );

This funcion tests if the named attribute is set for the node. If the attribute is specified, TRUE (1) will be returned, otherwise the returnvalue is FALSE (0).
hasAttributeNS 	

$boolean = $node->hasAttributeNS( $nsURI, $aname );

namespace version of hasAttribute
getChildrenByTagName 	

@nodes = $node->getChildrenByTagName($tagname);

The function gives direct access to all childnodes of the current node with the same tagname. It makes things a lot easier if you need to handle big datasets.
If this function is called in SCALAR context, it returns the number of Elements found.
getChildrenByTagNameNS 	

@nodes = $node->getChildrenByTagNameNS($nsURI,$tagname);

Namespace version of getChildrenByTagName.
If this function is called in SCALAR context, it returns the number of Elements found.
getElementsByTagName 	

@nodes = $node->;getElementsByTagName($tagname);

This function is part of the spec it fetches all descendants of a node with a given tagname. If one is as confused with tagname as I was, tagname is a qualified tagname which is in case of namespace useage prefix and local name
In SCALAR context this function returns a XML::LibXML::NodeList object.
getElementsByTagNameNS 	

@nodes = $node->getElementsByTagNameNS($nsURI,$localname);

Namespace version of getElementsByTagName as found in the DOM spec.
In SCALAR context this function returns a XML::LibXML::NodeList object.
getElementsByLocalName 	

@nodes = $node->getElementsByLocalName($localname);

This function is not found in the DOM specification. It is a mix of getElementsByTagName and getElementsByTagNameNS. It will fetch all tags matching the given local-name. This alows one to select tags with the same local name across namespace borders.
In SCALAR context this function returns a XML::LibXML::NodeList object.
appendWellBalancedChunk 	

$node->appendWellBalancedChunk( $chunk )

Sometimes it is nessecary to append a string coded XML Tree to a node. appendWellBalancedChunk will do the trick for you. But this is only done if the String is well-balanced.
Note that appendWellBalancedChunk() is only left for compatibility reasons. Implicitly it uses

 my $fragment = $parser->parse_xml_chunk( $chunk );
 $node->appendChild( $fragment );

This form is more explicit and makes it easier to control the flow of a script.
appendText 	

$node->appendText( $PCDATA );

alias for appendTextNode().
appendTextNode 	

$node->appendTextNode( $PCDATA );

This wrapper function lets you add a string directly to an element node.
appendTextChild 	

$node->appendTextChild( $childname , $PCDATA )

Somewhat similar with appendTextNode: It lets you set an Element, that contains only a text node directly by specifying the name and the text content.
setNamespace 	

$node->setNamespace( $nsURI , $nsPrefix, $activate )

setNamespace() allows one to apply a namespace to an element. The function takes three parameters: 1. the namespace URI, which is required and the two optional values prefix, which is the namespace prefix, as it should be used in child elements or attributes as well as the additional activate parameter.
The activate parameter is most useful: If this parameter is set to FALSE (0), the namespace is simply added to the namespacelist of the node, while the element's namespace itself is not altered. Nevertheless activate is set to TRUE (1) on default. In this case the namespace automatically is used as the nodes effective namespace. This means the namespace prefix is added to the node name and if there was a namespace already active for the node, this will be replaced (but not removed from the global namespace list)
The following example may clarify this:

 my $e1 = $doc->createElement("bar");
 $e1->setNamespace("http://foobar.org", "foo")

results

 <foo:bar xmlns:foo="http://foobar.org"/>

while

 my $e2 = $doc->createElement("bar");
 $e2->setNamespace("http://foobar.org", "foo",0)

results only

 <bar xmlns:foo="http://foobar.org"/>

By using $activate == 0 it is possible to apply multiple namepace declarations to a single element.
Alternativly you can call setAttribute() simply to declare a new namespace for a node, without activating it:

  $e2->setAttribute( "xmlns:foo", "http://bar.org" );

has the same result as

 $e2->setNamespace( "http://foobar.org", "foo", 0 );