diff --git a/packages/core/src/openbim/IDSSpecifications/index.ts b/packages/core/src/openbim/IDSSpecifications/index.ts
index d0e0619c2..2c86e6673 100644
--- a/packages/core/src/openbim/IDSSpecifications/index.ts
+++ b/packages/core/src/openbim/IDSSpecifications/index.ts
@@ -218,6 +218,9 @@ export class IDSSpecifications extends Component {
         specification.description = description;
         specification.instructions = instructions;
         specification.requirementsDescription = requirementsDescription;
+        const { minOccurs, maxOccurs } = applicability ?? {};
+        if (typeof minOccurs === "number") specification.minOccurs = minOccurs;
+        if (typeof maxOccurs === "number") specification.maxOccurs = maxOccurs;
         specification.applicability.add(...applicabilities);
         specification.requirements.add(...reqs);
         result.push(specification);
diff --git a/packages/core/src/openbim/IDSSpecifications/src/Specification.ts b/packages/core/src/openbim/IDSSpecifications/src/Specification.ts
index 96ce69af6..ad17aca8b 100644
--- a/packages/core/src/openbim/IDSSpecifications/src/Specification.ts
+++ b/packages/core/src/openbim/IDSSpecifications/src/Specification.ts
@@ -20,6 +20,18 @@ export class IDSSpecification implements IDSSpecificationData {
   description?: string;
   instructions?: string;
   requirementsDescription?: string;
+
+  /**
+   * Minimum number of applicable elements: `1` makes the specification
+   * required, `0` optional. Read from `minOccurs` of the applicability.
+   */
+  minOccurs = 1;
+
+  /**
+   * Maximum number of applicable elements: `0` makes the specification
+   * prohibited. Read from `maxOccurs` of the applicability.
+   */
+  maxOccurs: number | "unbounded" = "unbounded";
   applicability = new FRAGS.DataSet<IDSFacet>();
   requirements = new FRAGS.DataSet<IDSFacet>();
 
@@ -57,9 +69,40 @@ export class IDSSpecification implements IDSSpecificationData {
     modelIds: RegExp[],
     config: { skipIfFails: boolean } = { skipIfFails: true },
   ) {
-    const result: IDSCheckResult = new FRAGS.DataMap();
+    return (await this.run(modelIds, config)).result;
+  }
 
-    if (this.requirements.size === 0) return result;
+  /**
+   * Tests the models and also applies the specification's cardinality
+   * (`minOccurs` / `maxOccurs`): a required specification fails when too few
+   * elements are applicable, a prohibited one fails when any is, and an
+   * optional one may pass with none. Requirements of a prohibited
+   * specification are not evaluated.
+   *
+   * @returns `pass` is the specification-level verdict, `applicable` the number
+   * of applicable elements, and `result` the same per-element result as {@link test}.
+   */
+  async verify(
+    modelIds: RegExp[],
+    config: { skipIfFails: boolean } = { skipIfFails: true },
+  ) {
+    const { result, applicable } = await this.run(modelIds, config, true);
+    const max = this.maxOccurs === "unbounded" ? Infinity : this.maxOccurs;
+    let pass = applicable >= this.minOccurs && applicable <= max;
+    if (max > 0) {
+      for (const items of result.values()) {
+        for (const item of items.values()) if (!item.pass) pass = false;
+      }
+    }
+    return { pass, applicable, result };
+  }
+
+  private async run(
+    modelIds: RegExp[],
+    config: { skipIfFails: boolean },
+    skipProhibitedRequirements = false,
+  ) {
+    const result: IDSCheckResult = new FRAGS.DataMap();
 
     // Get applicable elements
     const entities: ModelIdMap = {};
@@ -70,6 +113,16 @@ export class IDSSpecification implements IDSSpecificationData {
 
     await Promise.all(applicabilityPromises);
 
+    let applicable = 0;
+    for (const ids of Object.values(entities)) applicable += ids.size;
+
+    if (
+      this.requirements.size === 0 ||
+      (skipProhibitedRequirements && this.maxOccurs === 0)
+    ) {
+      return { result, applicable };
+    }
+
     // Test applicable elements against requirements
     const requirementPromises = [];
     for (const requirement of this.requirements) {
@@ -77,7 +130,7 @@ export class IDSSpecification implements IDSSpecificationData {
     }
 
     await Promise.all(requirementPromises);
-    return result;
+    return { result, applicable };
   }
 
   /**
@@ -102,7 +155,7 @@ export class IDSSpecification implements IDSSpecificationData {
       : "";
 
     const xml = `<specification ifcVersion="${[...this.ifcVersion].join(" ")}" ${name} ${identifier} ${description} ${instructions}>
-      <applicability minOccurs="1" maxOccurs="unbounded">
+      <applicability minOccurs="${this.minOccurs}" maxOccurs="${this.maxOccurs}">
         ${[...this.applicability].map((facet) => facet.serialize("applicability")).join("\n")}
       </applicability>
       <requirements>
diff --git a/packages/core/src/openbim/IDSSpecifications/src/specification-cardinality.test.ts b/packages/core/src/openbim/IDSSpecifications/src/specification-cardinality.test.ts
new file mode 100644
index 000000000..6b4ebb727
--- /dev/null
+++ b/packages/core/src/openbim/IDSSpecifications/src/specification-cardinality.test.ts
@@ -0,0 +1,103 @@
+import * as FRAGS from "@thatopen/fragments";
+import * as fs from "fs";
+import * as path from "path";
+import { afterAll, beforeAll, describe, expect, it, vi } from "vitest";
+import type { Components } from "../../../index";
+import { loadSourceBundle } from "../../../../tests/source-bundle";
+
+// Needs the real `Components`: see `loadSourceBundle`.
+const OBC = await loadSourceBundle();
+
+const MODEL_ID = "cardinality";
+
+// `tests/fixtures/type-psets.ifc` holds six walls and no slabs.
+const ids = (
+  cardinality: string,
+  entity: string,
+  requirements = "",
+) => `<?xml version="1.0" encoding="UTF-8"?>
+<ids:ids xmlns:xs="http://www.w3.org/2001/XMLSchema" xmlns:ids="http://standards.buildingsmart.org/IDS">
+  <ids:info><ids:title>Cardinality</ids:title></ids:info>
+  <ids:specifications>
+    <ids:specification name="spec" ifcVersion="IFC4">
+      <ids:applicability ${cardinality}>
+        <ids:entity><ids:name><ids:simpleValue>${entity}</ids:simpleValue></ids:name></ids:entity>
+      </ids:applicability>
+      ${requirements}
+    </ids:specification>
+  </ids:specifications>
+</ids:ids>`;
+
+const waldo = `<ids:requirements><ids:attribute>
+  <ids:name><ids:simpleValue>Name</ids:simpleValue></ids:name>
+  <ids:value><ids:simpleValue>Waldo</ids:simpleValue></ids:value>
+</ids:attribute></ids:requirements>`;
+
+describe("IDSSpecification cardinality (minOccurs / maxOccurs)", () => {
+  let components: Components;
+  let model: FRAGS.SingleThreadedFragmentsModel;
+
+  beforeAll(async () => {
+    const importer = new FRAGS.IfcImporter();
+    const root = path.resolve(__dirname, "../../../..");
+    importer.wasm = {
+      path: `${path.resolve(root, "../../node_modules/web-ifc")}/`,
+      absolute: true,
+    };
+    const ifc = fs.readFileSync(
+      path.join(root, "tests", "fixtures", "type-psets.ifc"),
+    );
+    const bytes = await importer.process({
+      bytes: new Uint8Array(ifc),
+      raw: true,
+    });
+    model = new FRAGS.SingleThreadedFragmentsModel(MODEL_ID, bytes, true);
+    components = new OBC.Components();
+    vi.spyOn(
+      components.get(OBC.FragmentsManager),
+      "list",
+      "get",
+    ).mockReturnValue(new Map([[MODEL_ID, model]]) as never);
+  }, 60_000);
+
+  afterAll(() => {
+    vi.restoreAllMocks();
+    components?.dispose();
+    model?.dispose();
+  });
+
+  const verify = async (xml: string) => {
+    const [spec] = components.get(OBC.IDSSpecifications).load(xml);
+    return spec.verify([new RegExp(MODEL_ID)], { skipIfFails: false });
+  };
+
+  const required = 'minOccurs="1" maxOccurs="unbounded"';
+  const optional = 'minOccurs="0" maxOccurs="unbounded"';
+  const prohibited = 'minOccurs="0" maxOccurs="0"';
+
+  it("required: fails when nothing is applicable", async () => {
+    expect((await verify(ids(required, "IFCSLAB", waldo))).pass).toBe(false);
+  });
+
+  it("required: applicable elements are still judged by the requirements", async () => {
+    expect((await verify(ids(required, "IFCWALL", waldo))).pass).toBe(false);
+  });
+
+  it("optional: may pass when nothing is applicable", async () => {
+    expect((await verify(ids(optional, "IFCSLAB", waldo))).pass).toBe(true);
+  });
+
+  it("prohibited: fails when the applicability matches", async () => {
+    const r = await verify(ids(prohibited, "IFCWALL"));
+    expect(r.applicable).toBe(6);
+    expect(r.pass).toBe(false);
+  });
+
+  it("prohibited: passes when the applicability does not match", async () => {
+    expect((await verify(ids(prohibited, "IFCSLAB"))).pass).toBe(true);
+  });
+
+  it("prohibited: does not throw when requirements are (invalidly) given", async () => {
+    expect((await verify(ids(prohibited, "IFCSLAB", waldo))).pass).toBe(true);
+  });
+});
diff --git a/packages/core/src/openbim/IDSSpecifications/src/specification-occurs.test.ts b/packages/core/src/openbim/IDSSpecifications/src/specification-occurs.test.ts
new file mode 100644
index 000000000..69caae36b
--- /dev/null
+++ b/packages/core/src/openbim/IDSSpecifications/src/specification-occurs.test.ts
@@ -0,0 +1,50 @@
+import { describe, expect, it } from "vitest";
+import { loadSourceBundle } from "../../../../tests/source-bundle";
+
+// Needs the real `Components`: see `loadSourceBundle`.
+const OBC = await loadSourceBundle();
+
+const ids = (occurs: string) => `<?xml version="1.0" encoding="UTF-8"?>
+<ids:ids xmlns:xs="http://www.w3.org/2001/XMLSchema" xmlns:ids="http://standards.buildingsmart.org/IDS">
+  <ids:info><ids:title>Occurs</ids:title></ids:info>
+  <ids:specifications>
+    <ids:specification name="spec" ifcVersion="IFC4">
+      <ids:applicability ${occurs}>
+        <ids:entity><ids:name><ids:simpleValue>IFCWALL</ids:simpleValue></ids:name></ids:entity>
+      </ids:applicability>
+    </ids:specification>
+  </ids:specifications>
+</ids:ids>`;
+
+describe("IDSSpecification minOccurs / maxOccurs", () => {
+  const roundTrip = (occurs: string) => {
+    const manager = new OBC.Components().get(OBC.IDSSpecifications);
+    const [spec] = manager.load(ids(occurs));
+    const xml = manager.export({ title: "t" }, [spec]);
+    const [again] = manager.load(xml);
+    return { spec, xml, again };
+  };
+
+  it("required (1, unbounded) is the default", () => {
+    const { spec } = roundTrip("");
+    expect([spec.minOccurs, spec.maxOccurs]).toEqual([1, "unbounded"]);
+  });
+
+  it("optional (0, unbounded) survives load and export", () => {
+    const { spec, xml, again } = roundTrip(
+      'minOccurs="0" maxOccurs="unbounded"',
+    );
+    expect([spec.minOccurs, spec.maxOccurs]).toEqual([0, "unbounded"]);
+    expect(xml).toContain(
+      '<applicability minOccurs="0" maxOccurs="unbounded">',
+    );
+    expect([again.minOccurs, again.maxOccurs]).toEqual([0, "unbounded"]);
+  });
+
+  it("prohibited (0, 0) survives load and export", () => {
+    const { spec, xml, again } = roundTrip('minOccurs="0" maxOccurs="0"');
+    expect([spec.minOccurs, spec.maxOccurs]).toEqual([0, 0]);
+    expect(xml).toContain('<applicability minOccurs="0" maxOccurs="0">');
+    expect([again.minOccurs, again.maxOccurs]).toEqual([0, 0]);
+  });
+});