Add a new preserveDocumentType parser option

[rgrove]

When true, an XmlDocumentType node representing a document type declaration (if there is one) will be included in the parsed document. When false, any document type declaration encountered will be discarded. The default is false, which matches the behavior of previous versions.

Note that the parser only includes the document type declaration in the node tree; it doesn't actually validate the document against the DTD, load external DTDs, or resolve custom entity references.

This option is useful if you want to preserve the document type declaration when later serializing a document back to XML. Previously, the document type declaration was always discarded, which meant that if you parsed a document with a document type declaration and then serialized it, the original document type declaration would be lost.

const { parseXml } = require('@rgrove/parse-xml');

let xml = '<!DOCTYPE root SYSTEM "root.dtd"><root />';
let doc = parseXml(xml, { preserveDocumentType: true });

console.log(doc.children[0].toJSON());
// => { type: 'doctype', name: 'root', systemId: 'root.dtd' }

xml = '<!DOCTYPE kittens [<!ELEMENT kittens (#PCDATA)>]><kittens />';
doc = parseXml(xml, { preserveDocumentType: true });

console.log(doc.children[0].toJSON());
// => {
//   type: 'doctype',
//   name: 'kittens',
//   internalSubset: '<!ELEMENT kittens (#PCDATA)>'
// }

/cc @wooorm

[wooorm]

😍