diff --git a/src/competencies/oNet.ts b/src/competencies/oNet.ts
index 6d21e9b..eda4f8b 100644
--- a/src/competencies/oNet.ts
+++ b/src/competencies/oNet.ts
@@ -2,7 +2,7 @@
  * A selection of abilities and skills from the O*NET 24.3 Database, sponsored
  * by the U.S. Department of Labor, Employment and Training Administration.
  *
- * The database is licensed under a Creative Commons Attribution 4.0
+ * The database is provided under a Creative Commons Attribution 4.0
  * International License.
  *
  * {@link https://www.onetcenter.org/license_db.html}
diff --git a/src/education/institutions/index.ts b/src/education/institutions/index.ts
index 43c162d..eb9d313 100644
--- a/src/education/institutions/index.ts
+++ b/src/education/institutions/index.ts
@@ -21,7 +21,20 @@ export const all: EducationInstitution[] = [
 ].flat();
 
 interface FilterProps {
+  /**
+   * Limit institutions to those that operate in at least one of the specified
+   * countries.
+   *
+   * Omit this filter to return institutions from all countries.
+   */
   country?: CountryCode | CountryCode[];
+
+  /**
+   * Limit institutions to those that offer an education programme that
+   * corresponds to at least one of the specified ISCED 2011 levels.
+   *
+   * Omit this filter to return institutions regardless of education level.
+   */
   level?: EducationLevel | EducationLevel[];
 }
 
diff --git a/src/education/institutions/row.ts b/src/education/institutions/row.ts
index a0a9a18..229661d 100644
--- a/src/education/institutions/row.ts
+++ b/src/education/institutions/row.ts
@@ -381,6 +381,6 @@ export const universities: EducationInstitution[] = ([
   },
 ] as const).map((props) =>
   Object.assign(props, {
-    levels: [6, 7, 8] as const,
-  }),
+    levels: [6, 7, 8],
+  } as const),
 );
diff --git a/src/filter.test.ts b/src/filter.test.ts
index 5a39fa5..6dbeebe 100644
--- a/src/filter.test.ts
+++ b/src/filter.test.ts
@@ -5,40 +5,48 @@ describe('createSubsetMatcher', () => {
     const match = createSubsetMatcher();
 
     it.each([
-      ['no elements', []],
-      ['undefined', [undefined]],
-      ['null', [null]],
-      ['empty string', ['']],
-      ['non-empty string', ['abc123']],
-    ])('allows array with %s', (_, value) => expect(match(value)).toBe(true));
+      ['undefined', undefined],
+      ['null', null],
+      ['empty string', ''],
+      ['non-empty string', 'abc123'],
+      ['array with no elements', []],
+      ['array with undefined', [undefined]],
+      ['array with null', [null]],
+      ['array with empty string', ['']],
+      ['array with non-empty string', ['abc123']],
+    ])('allows %s', (_, value) => expect(match(value)).toBe(true));
   });
 
   describe('given one value', () => {
     const match = createSubsetMatcher(1);
 
     it.each([
-      ['matching element only', [1]],
-      ['matching elements only', [1, 1]],
-      ['mix of matching and non-matching elements', [2, 1, 3]],
-    ])('allows array with %s', (_, value) => expect(match(value)).toBe(true));
+      ['matching element', 1],
+      ['array with matching element only', [1]],
+      ['array with matching elements only', [1, 1]],
+      ['array with matching and non-matching elements', [2, 1, 3]],
+    ])('allows %s', (_, value) => expect(match(value)).toBe(true));
 
     it.each([
-      ['no elements', []],
-      ['non-matching elements only', [3, 2]],
-    ])('denies array with %s', (_, value) => expect(match(value)).toBe(false));
+      ['non-matching element', 2],
+      ['array with no elements', []],
+      ['array with non-matching elements only', [3, 2]],
+    ])('denies %s', (_, value) => expect(match(value)).toBe(false));
   });
 
   describe('given two values', () => {
     const match = createSubsetMatcher(['a', 'b']);
 
     it.each([
-      ['first matching element only', ['a']],
-      ['second matching element only', ['b']],
-      ['both matching elements', ['b', 'a']],
-      ['mix of matching and non-matching elements', ['c', 'a', 'd', 'b']],
-    ])('allows array with %s', (_, value) => expect(match(value)).toBe(true));
+      ['matching element', 'a'],
+      ['array with first matching element only', ['a']],
+      ['array with second matching element only', ['b']],
+      ['array with both matching elements', ['b', 'a']],
+      ['array with matching and non-matching elements', ['c', 'a', 'd', 'b']],
+    ])('allows %s', (_, value) => expect(match(value)).toBe(true));
 
     it.each([
+      ['non-matching element', 'c'],
       ['no elements', []],
       ['non-matching elements only', ['d', 'c']],
     ])('denies array with %s', (_, value) => expect(match(value)).toBe(false));
diff --git a/src/filter.ts b/src/filter.ts
index 85020c0..e43f22e 100644
--- a/src/filter.ts
+++ b/src/filter.ts
@@ -1,11 +1,15 @@
+const isArray = <T>(input: T | ReadonlyArray<T>): input is ReadonlyArray<T> =>
+  Array.isArray(input);
+
 export const createSubsetMatcher = <T>(
-  value?: T | T[],
-): ((inputs: ReadonlyArray<T>) => boolean) => {
+  value?: T | ReadonlyArray<T>,
+): ((input: T | ReadonlyArray<T>) => boolean) => {
   if (typeof value === 'undefined') {
     return () => true;
   }
 
-  const values = new Set(Array.isArray(value) ? value : [value]);
+  const values = new Set(isArray(value) ? value : [value]);
 
-  return (inputs) => inputs.some((input) => values.has(input));
+  return (input) =>
+    isArray(input) ? input.some((i) => values.has(i)) : values.has(input);
 };
diff --git a/src/readme.ts b/src/readme.ts
index ed05bdb..a3acde3 100644
--- a/src/readme.ts
+++ b/src/readme.ts
@@ -2,8 +2,6 @@
 
 import { fakeHr } from '.';
 
-console.log('hello there');
-
 console.log(fakeHr.competencies.all[0]);
 
 console.log(fakeHr.education.institutions.all[0]);