Part the source into adf/ and markdown/ ahead of the parser

src/adf/mark-attributes.ts

@@ -0,0 +1,19 @@
+import type { AttributeVocabulary } from './attribute-vocabulary.ts'
+
+export const markAttributes = {
+  border: { color: 'string', size: 'number' },
+  code: {},
+  em: {},
+  link: { href: 'string', title: 'string' },
+  strike: {},
+  strong: {},
+  subsup: { type: 'string' },
+  textColor: { color: 'string' },
+  underline: {},
+} satisfies Readonly<Record<string, AttributeVocabulary>>
+
+export type MarkType = keyof typeof markAttributes
+
+export function isMarkType(type: string): type is MarkType {
+  return Object.hasOwn(markAttributes, type)
+}