diff --git a/src/parser/parsedHedSubstring.d.ts b/src/parser/parsedHedSubstring.d.ts
new file mode 100644
index 00000000..d11152cf
--- /dev/null
+++ b/src/parser/parsedHedSubstring.d.ts
@@ -0,0 +1,40 @@
+declare abstract class ParsedHedSubstring {
+  /**
+   * The original pre-parsed version of the HED tag.
+   */
+  originalTag: string
+  /**
+   * The bounds of the HED tag in the original HED string.
+   */
+  originalBounds: number[]
+
+  /**
+   * Constructor.
+   * @param originalTag The original HED tag.
+   * @param originalBounds The bounds of the HED tag in the original HED string.
+   */
+  protected constructor(originalTag: string, originalBounds: number[])
+
+  /**
+   * Nicely format this substring. This is left blank for the subclasses to override.
+   *
+   * This is left blank for the subclasses to override.
+   *
+   * @param long Whether the tags should be in long form.
+   */
+  public abstract format(long: boolean): string
+
+  /**
+   * Get the normalized version of the object.
+   */
+  public abstract get normalized(): string
+
+  /**
+   * Override of {@link Object.prototype.toString}.
+   *
+   * @returns The original form of this HED substring.
+   */
+  public toString(): string
+}
+
+export = ParsedHedSubstring
diff --git a/src/parser/parsedHedSubstring.js b/src/parser/parsedHedSubstring.js
index 27ea6a4b..46136ef8 100644
--- a/src/parser/parsedHedSubstring.js
+++ b/src/parser/parsedHedSubstring.js
@@ -2,53 +2,11 @@
  * A parsed HED substring.
  */
 export class ParsedHedSubstring {
-  /**
-   * The original pre-parsed version of the HED tag.
-   * @type {string}
-   */
-  originalTag
-  /**
-   * The bounds of the HED tag in the original HED string.
-   * @type {int[]}
-   */
-  originalBounds
-
-  /**
-   * Constructor.
-   * @param {string} originalTag The original HED tag.
-   * @param {number[]} originalBounds The bounds of the HED tag in the original HED string.
-   */
   constructor(originalTag, originalBounds) {
     this.originalTag = originalTag
     this.originalBounds = originalBounds
   }
 
-  /**
-   * Nicely format this substring. This is left blank for the subclasses to override.
-   *
-   * This is left blank for the subclasses to override.
-   *
-   * @param {boolean} long - Whether the tags should be in long form.
-   * @returns {string}
-   * @abstract
-   */
-  format(long = true) {}
-
-  /**
-   * Get the normalized version of the object.
-   *
-   * @returns {string}
-   * @abstract
-   */
-  get normalized() {
-    return ''
-  }
-
-  /**
-   * Override of {@link Object.prototype.toString}.
-   *
-   * @returns {string} The original form of this HED substring.
-   */
   toString() {
     return this.originalTag
   }