diff --git a/packages/mongodb-ns/src/index.spec.ts b/packages/mongodb-ns/src/index.spec.ts
index a0b89ab37..5c0f74dc6 100644
--- a/packages/mongodb-ns/src/index.spec.ts
+++ b/packages/mongodb-ns/src/index.spec.ts
@@ -231,6 +231,28 @@ describe('ns', function () {
     assert.equal(ns('abc.').database, 'abc');
   });
 
+  describe('shared classification regexps', function () {
+    it('keeps an implied lastIndex of 0 between parses', function () {
+      // The RegExps were moved up to the module scope and are shared across invocations
+      // if one were to add 'g' or 'y' they would become stateful
+      // these tests will fail if the RegExps become stateful
+      assert(ns('__mdb_internal_a.x').isInternal());
+      assert(ns('__mdb_internal_b.x').isInternal());
+
+      assert(ns('a.system.javascript').isSystem());
+      assert(ns('b.system.typescript').isSystem());
+
+      assert(ns('c.local.oplog.rs').isOplog());
+      assert(ns('d.local.oplog.$main').isOplog());
+
+      assert.equal(ns('foo').validDatabaseName, true);
+      assert.equal(ns('bar').validDatabaseName, true);
+
+      assert(ns('p.mycol').validCollectionName);
+      assert(ns('q.yourcol').validCollectionName);
+    });
+  });
+
   describe('sorting', function () {
     it('should sort them', function () {
       const names = [
diff --git a/packages/mongodb-ns/src/index.ts b/packages/mongodb-ns/src/index.ts
index 0ac0aec72..a2fa020dd 100644
--- a/packages/mongodb-ns/src/index.ts
+++ b/packages/mongodb-ns/src/index.ts
@@ -1,26 +1,111 @@
+/**
+ * A MongoDB namespace (the `database.collection` string) and the
+ * classification flags derived from it.
+ */
 type NS = {
+  /**
+   * The full namespace string, e.g. `'mydb.mycollection'`.
+   */
   ns: string;
+  /**
+   * Index of the first `.` in `ns`, or `-1` when there is no dot.
+   */
   dotIndex: number;
+  /**
+   * Everything before the first `.` in `ns`
+   * or the whole string when there is no dot.
+   */
   database: string;
+  /**
+   * Everything after the first `.` in `ns`, or `''` when there is no dot.
+   */
   collection: string;
+  /**
+   * @see isSystem
+   */
   system: boolean;
+  /**
+   * Whether this is a system-generated collection: the collection name is a
+   * `system.*` collection (anything beginning with `system.` except
+   * `system.profile` itself) or an `enxcol_.` queryable-encryption
+   * collection.
+   */
   isSystem(): boolean;
+  /**
+   * @see isOplog
+   */
   oplog: boolean;
+  /**
+   * Whether the namespace is one of the two oplog namespaces,
+   * `local.oplog.$main` or `local.oplog.rs`.
+   */
   isOplog(): boolean;
+  /**
+   * @see isCommand
+   */
   command: boolean;
+  /**
+   * Whether the collection is the command collection `$cmd` or begins with
+   * `$cmd.sys`.
+   */
   isCommand(): boolean;
+  /**
+   * @see isSpecial
+   */
   special: boolean;
+  /**
+   * Whether the namespace is not an ordinary database/collection pair: set
+   * when any of `oplog`, `command`, `system`, `internal` is true or the
+   * database is `config`.
+   */
   isSpecial(): boolean;
+  /**
+   * One level looser than `special`: true when `special` is true, or the
+   * database is `local` or `admin`. `NS.sort` uses it to keep these
+   * namespaces at the end of a sorted list.
+   */
   specialish: boolean;
+  /**
+   * @see isNormal
+   */
   normal: boolean;
+  /**
+   * Whether the namespace is an oplog, or when `ns` contains no `$` character
+   * at all. (Despite the name, this includes the oplog.)
+   */
   isNormal(): boolean;
+  /**
+   * @see isInternal
+   */
   internal: boolean;
+  /**
+   * Whether the database is an internal database - its name matches
+   * `/^__mdb_internal_\w/`. See the MongoDB Atlas "internal databases" docs.
+   *
+   * @see https://www.mongodb.com/docs/atlas/reference/internal-database/#internal-databases
+   */
   isInternal(): boolean;
+  /**
+   * True when the database is a valid database name, i.e. it contains no
+   * backslash, `/`, `"`, `.` or space, and is at most
+   * `NS.MAX_DATABASE_NAME_LENGTH` (128) characters long.
+   */
   validDatabaseName: boolean;
+  /**
+   * True when the collection name is non-empty and either the namespace is an
+   * oplog or the name contains no NUL byte and no `$`.
+   */
   validCollectionName: boolean;
+  /**
+   * @deprecated An approximate equivalent to Java's hashCode that does not work for db names longer than 30 characters.
+   *
+   * Hash of the database portion of `ns`, computed in the constructor from
+   * the characters up to (and excluding) the first `.`.
+   */
   databaseHash: number;
+  /** The namespace string itself (`ns`). */
   toString(): string;
-  // Assigned in the constructor, but will always be undefined
+  /** Always `undefined` - reserved, never implemented. */
   isConf(): undefined;
 };
 
@@ -32,6 +117,12 @@ type NSConstructor = {
   sort(namespaces: (string | NS)[]): typeof namespaces;
 };
 
+const INTERNAL_DATABASE_REGEXP = /^__mdb_internal_\w/;
+const SYSTEM_COLLECTION_REGEXP = /^(?:system(?!\.profile$).*|enxcol_)\./;
+const OPLOG_REGEXP = /local\.oplog\.(\$main|rs)/;
+const VALID_DATABASE_NAME_REGEXP = /^[^\\/". ]*$/;
+const VALID_COLLECTION_NAME_REGEXP = /^[^\0$]*$/;
+
 // eslint-disable-next-line complexity
 const NS: NSConstructor = function (this: NS, ns: string | NS): NS {
   ns = ns.toString();
@@ -49,12 +140,11 @@ const NS: NSConstructor = function (this: NS, ns: string | NS): NS {
     this.collection = ns.slice(this.dotIndex + 1);
   }
 
-  // https://www.mongodb.com/docs/atlas/reference/internal-database/#internal-databases
-  this.internal = /^__mdb_internal_\w/.test(this.database);
+  this.internal = INTERNAL_DATABASE_REGEXP.test(this.database);
 
-  this.system = /^(?:system(?!\.profile$).*|enxcol_)\./.test(this.collection);
+  this.system = SYSTEM_COLLECTION_REGEXP.test(this.collection);
 
-  this.oplog = /local\.oplog\.(\$main|rs)/.test(ns);
+  this.oplog = OPLOG_REGEXP.test(ns);
 
   this.command =
     this.collection === '$cmd' || this.collection.indexOf('$cmd.sys') === 0;
@@ -66,7 +156,7 @@ const NS: NSConstructor = function (this: NS, ns: string | NS): NS {
     this.internal;
 
   this.specialish =
-    this.special || ['local', 'admin'].indexOf(this.database) > -1;
+    this.special || this.database === 'local' || this.database === 'admin';
 
   this.normal = this.oplog || this.ns.indexOf('$') === -1;
 
@@ -75,11 +165,11 @@ const NS: NSConstructor = function (this: NS, ns: string | NS): NS {
    * `*<>:|?`
    */
   this.validDatabaseName =
-    new RegExp('^[^\\\\/". ]*$').test(this.database) &&
+    VALID_DATABASE_NAME_REGEXP.test(this.database) &&
     this.database.length <= NS.MAX_DATABASE_NAME_LENGTH;
   this.validCollectionName =
     this.collection.length > 0 &&
-    (this.oplog || /^[^\0$]*$/.test(this.collection));
+    (this.oplog || VALID_COLLECTION_NAME_REGEXP.test(this.collection));
 
   this.databaseHash = 7;
   this.ns.split('').every((c, i) => {