xmlTree: An internal, updatable DOM object for building XML trees

Description

This is a mutable object (implemented via a closure) for representing an XML tree, in the same spirit as xmlOutputBuffer and xmlOutputDOM but that uses the internal structures of libxml. This can be used to create a DOM that can be constructed in R and exported to another system such as XSLT (http://www.omegahat.org/Sxslt)

Usage

xmlTree(tag, attrs = NULL, dtd=NULL, namespaces=list())

Arguments

tag

the tagname of the top-level element. This is basically ignored!

attrs

attributes for the top-level node, in the form of a named vector or list.

dtd

the name of the external DTD for this document. See newXMLDoc

namespaces

a named character vector with each element giving the name space identifier and the corresponding URI, \ e.g c(shelp = "http://www.omegahat.org/XML/SHelp")

Value

An object of class XMLInternalDOM that extends XMLOutputStream and has the same interface (i.e. ``methods'') as xmlOutputBuffer and xmlOutputDOM. Each object has methods for adding a new XML tag, closing a tag, adding an XML comment, and retrieving the contents of the tree.
addTagcreate a new tag at the current position, optionally leaving it as the active open tag to which new nodes will be added as children
closeTagclose the currently active tag making its parent the active element into which new nodes will be added.
addCommentadd an XML comment node as a child of the active node in the document.
valueretrieve an object representing the XML tree. See saveXML to serialize the contents of the tree.
adddegenerate method in this context.

Details

This creates a collection of functions that manipulate a shared state to build and maintain an XML tree in C-level code.

References

http://www.w3.org/XML, http://www.xmlsoft.org, http://www.omegahat.org

Examples

Run this code

tr <- xmlTree("Duncan")
  tr$addTag("name", attrs=c(a=1,b="xyz"), close=FALSE)
    tr$addTag("first", "Larry")
    tr$addTag("last", "User")
  tr$closeTag()
  tr$value()
  cat(saveXML(tr$value()))

  tr <- xmlTree("CDataTest")
  tr$addTag("top", close=FALSE)
  tr$addCData("x <- list(1, a='&');
x[[2]]")
  tr$addPI("S", "plot(1:10)")
  tr$closeTag()
  cat(saveXML(tr$value()))

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