Initial

module/data/fields/_module.mjs

@@ -1,3 +1,4 @@
 export { default as FormulaField } from './formulaField.mjs';
 export { default as ForeignDocumentUUIDField } from './foreignDocumentUUIDField.mjs';
 export { default as ForeignDocumentUUIDArrayField } from './foreignDocumentUUIDArrayField.mjs';
+export { default as ItemLinksField } from './itemLinksField.mjs';

module/data/fields/itemLinksField.mjs

@@ -0,0 +1,32 @@
+export default class ItemLinksField extends foundry.data.fields.TypedObjectField {
+    /**
+     * @param {DataFieldOptions} [options]    Options which configure the behavior of the field.
+     * @param {DataFieldContext} [context]    Additional context which describes the field
+     */
+    constructor(options, context) {
+        super(
+            new foundry.data.fields.StringField({
+                choices: CONFIG.DH.ITEM.featureSubTypes,
+                nullable: true,
+                initial: null
+            }),
+            options,
+            context
+        );
+    }
+
+    /** @inheritDoc */
+    static get _defaults() {
+        return mergeObject(super._defaults, { validateKey: this.validateKey });
+    }
+
+    /**
+     * @param {Object} [value]    The candidate object to be added.
+     */
+    static validateKey(value) {
+        return true;
+        const parsed = foundry.utils.parseUuid(value);
+        if (!parsed || parsed.type !== CONFIG.Item.documentClass.documentName) return false;
+        if (!foundry.packages.BasePackage.validateId(parsed.documentId)) return false;
+    }
+}