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A drop-in replacement for the xml2 package in Renjin. Note that this replacement package is currently by no means fully functional. Check the NAMESPACE file to get an impression of which functions are available. In the remainder of this README, the term xml2 refers to the original R package authored by Wickham et al.
The xml2 package uses S3 classes to represent an XML document and its nodes: xml_document and xml_node. There is a
third class xml_nodeset to represent a list of nodes.
Objects of class xml_document inherit from xml_node therefore objects from these two classes have almost the same
structure: both are a list with two named elements: node and doc. An XML document is essentially represented by the
root node. The node element will be the pointer to the node and the doc element will be a pointer to the document.
The latter is a way to keep track of the document which 'owns' the node, but Java allows you to obtain a reference to
this document from a node.
Before version 1.0.0 of the xml2 package, the read_xml()
function passed the XML_PARSE_NOBLANKS option to libxml2 by default. Since version 1.0.0, the function has an
options argument to control the parser options and options="NOBLANKS" is the default value. The effect of this
option is to remove blank nodes, but the exact definition used by libxml2 for a blank node is not clear, see e.g.
this discussion.
Java has an option to remove certain 'ignorable whitespace' using setIgnoringElementContentWhitespace when the parser
is created, but the
documentation
clearly states that this option can only be used in validating mode. At a minimum, this requires a DTD to be present in
the XML document.
All this means that behavior between xml2 and renjin-xml2 may be different when dealing with blank nodes.
The xml2 package includes a function read_html() to parse HTML files. HTML looks like XML, but browsers will accept HTML
documents which are invalid or malformed XML documents. The package uses the
HTMLparser module from the libxml2 C library to parse (and fix)
HTML documents. Java built-in XML processors do not have such an HTML parser, therefore the renjin-xml2 package uses
the jsoup Java library. In particular, we use jsoup to parse the document and convert it to a
well-formed XML document using the outerHtml()
method.
The xml2 package is licensed as GPL version 2 or later and this replacement package has the same license. See the LICENSE file for the full text of the license.