getTemplate: Find the template to process a node

In omegahat/Sxslt: R interface to libxslt

Find the template to process a node

Description

This function and methods are intended to help understand and debug XSL processing by allowing the caller to query which XSL template will be used to process a particular node.

There are several different methods which attempt to make it both convenient and efficient to invoke. One can specify the style sheet and node by name, i.e. a URL for the style sheet document and a string giving the name of the node of interest. Alternatively, one can parse the style sheet and pass this internal representation. If one is querying multiple templates within the same style sheet, this avoids re-parsing the style sheet each time.

When dealing with nodes with name spaces, you create the XMLInternalNode, e.g. via newXMLNode, and give it the name space definitions. Alternatively, you can take a node from an existing XML document.

Finally, in the process of an XSL transformation, an R function which has a reference to the XMLXPathParserContext-class object for that XSL transformation can get the template for an arbitrary node from that XSL context which has access to the style sheet in effect.

Usage

getTemplate(ctxt, node, mode = character())

Arguments

ctxt	the object that identifies the XSL style sheet. This can be one of several different types of object. It can be a URL/file name of style sheet, a pre-parsed style sheet, an XMLInternalDocument obtained by reading the XSL document into R (using xmlParse), or an XMLXPathContext ?????
node	an object identifying the XML node whose corresponding applicable template is to be found in the style sheet. This can be a string giving the node name or an actual internal node of class XMLInternalNode created via newXMLNode or obtained from a parsed XML document.
mode	a character string specifying the XSL mode to use when looking for the template. This allows us to emulate how XSL transformations work via <xsl:apply-templates mode="val"/> when searching for the matching template.

Value

The basic return value is an object of class XSLTemplateDescription-class. If the parsed style sheet was not supplied by the user, an object of class XSLCopiedTemplateDescription is returned which has certain fields converted to an R representation rather than left as references to C-level data structures that will be garbage collected. XSLCopiedTemplateDescription-class is a "sub-class" of XSLTemplateDescription-class. Both of these classes are currently in S3-style form.

Note

We could copy the node and style sheet when it would be garbage collected but it is not clear how people will want to use this information, e.g. apply a template.

Author(s)

Duncan Temple Lang

References

~put references to the literature/web site here ~

See Also

xsltParseStyleSheet xmlParse

Examples

  
    # A query to see which template handles article.
   #XXX Problem
  temp = getTemplate("http://www.omegahat.org/XDynDocs/XSL/html.xsl", "article")

    # Query a node with a name space so have to create the node
    # (The node does get copied as it has no document which is needed
    # during the creation of the XSL context)
  library(XML)
  node = newXMLNode("r:code", namespaceDefinitions = c(r = "http://www.r-project.org"))
  rcode = getTemplate("http://www.omegahat.org/XDynDocs/XSL/html.xsl", node)

  rcode
  docName(rcode)
  rcode$location
  cat(rcode$node)
 

    # Instead of parsing the style sheet each time, do it once and do
    # multiple queries
  html.sty = xsltParseStyleSheet("http://www.omegahat.org/XDynDocs/XSL/html.xsl")

  rcode = getTemplate(html.sty, 
                      newXMLNode("r:code", namespaceDefinitions = c(r = "http://www.r-project.org")))

  templates = lapply(c("latex", "docbook", "ulink"), function(x)  getTemplate(html.sty, x))
  sapply(templates, docName)

omegahat/Sxslt documentation built on Jan. 17, 2024, 6:44 p.m.