# These are classes and facilities for referring to a DTD for the
# DOCTYPE field of an XML document

setClass("Doctype", representation(name = "character",
                                   system = "character",
                                   public = "character"))

Doctype =
function(system = "", public = "", name = "")
{
  new("Doctype", name = name, system = system, public = public)
}

setAs("Doctype", "character",
       function(from) {

         if(sum(nchar(from@public), nchar(from@system)))
            extra = c("SYSTEM", ifelse(from@public != "", dQuote(from@public), ""), 
                                ifelse(from@system != "", dQuote(from@system), ""))
         paste("<!DOCTYPE", from@name, paste(extra, collapse = " "), ">")
       })