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# These are classes and facilities for referring to a DTD for the
# DOCTYPE field of an XML document
# The 4 elements are + or -//creator//name of what is being referenced//language (decribed by ISO639)
# See XML Elements of Style by Simon St. Laurent.
validatePublicIdentifier =
function(object)
{
els = strsplit(object, "//")[[1]]
if(length(els) != 4)
return("a PUBLIC identifier must have 4 parts, separated by //")
if(! (els[1] %in% c("+", "-")))
return("first element of PUBLIC identifier must be + or -")
TRUE
}
setClass("DTDPublicIdentifier",
contains = "character",
validity = validatePublicIdentifier)
# name is the node name for the top-level node.
# system and public identify the DTD.
setClass("Doctype", representation(name = "character",
system = "character",
public = "character"),
validity = function(object) {
if(length(nchar(object@system)) > 0 && length(object@public) > 0)
return("only one of system and public can be specified")
if(length(object@public) > 0 && length(object@public) != 2)
return("the public part of the Doctype must have exactly 2 elements.")
if(length(object@public) > 0) {
tmp = validatePublicIdentifier(object@public[1])
if(!is.logical(tmp))
return(tmp)
}
TRUE
})
Doctype =
function(system = character(), public = character(), name = "")
{
if(length(public) == 1 && length(system) > 0) {
public = c(public, system)
system = character()
}
new("Doctype", name = name, system = system, public = public)
}
ddQuote =
function(x)
{
if(length(x) == 0)
return(character())
paste('"', x, '"', sep = "")
}
setAs("Doctype", "character",
function(from) {
extra = character()
if(sum(nchar(from@public), nchar(from@system))) {
if(length(from@system))
extra = c(extra, "SYSTEM", ddQuote(from@system))
if(length(from@public))
extra = c(extra, "PUBLIC", ddQuote(from@public))
}
paste("<!DOCTYPE", from@name, paste(extra, collapse = " "), ">")
})
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