Add a new preserveXmlDeclaration parser option

[rgrove]

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

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

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

let xml = '<?xml version="1.0" encoding="UTF-8"?><root />';
let doc = parseXml(xml, { preserveXmlDeclaration: true });

console.log(doc.children[0].toJSON());
// => { type: 'xmldecl', version: '1.0', encoding: 'UTF-8' }

This is the first half of #30.

/cc @wooorm

[wooorm]

Very cool!!