DOMImplementation: createDocumentType() メソッド

createDocumentType(qualifiedNameStr, publicId, systemId)

const dt = document.implementation.createDocumentType(
  "svg:svg",
  "-//W3C//DTD SVG 1.1//EN",
  "http://www.w3.org/Graphics/SVG/1.1/DTD/svg11.dtd",
);
const d = document.implementation.createDocument(
  "http://www.w3.org/2000/svg",
  "svg:svg",
  dt,
);
alert(d.doctype.publicId); // -//W3C//DTD SVG 1.1//EN