diff --git a/generated_template.d.ts b/generated_template.d.ts
index f49d9f8..bbde75d 100755
--- a/generated_template.d.ts
+++ b/generated_template.d.ts
@@ -8,10 +8,23 @@ export interface Location {
   offset: number;
 }

+type AnyObject = {
+    readonly [K: string]: unknown;
+}
+
+export interface Source extends AnyObject {
+    /**
+     * This function is used when trace is set to true to do ???
+     * TODO: Better documentation. I don't know what's going on here entirely to be honest.
+     */
+    offset?: (location: Location) => Location
+}
+
+
 /** The `start` and `end` position's of an object within the source. */
 export interface LocationRange {
   /** Any object that was supplied to the `parse()` call as the `grammarSource` option. */
-  source: any;
+  source: Source;
   /** Position at the beginning of the expression. */
   start: Location;
   /** Position after the end of the expression. */
@@ -23,7 +36,7 @@ export interface LiteralExpectation {
   text: string;
   ignoreCase: boolean;
 }
-export interface ClassParts extends Array<string | ClassParts> {}
+export interface ClassParts extends Array<string | [string, string]> {}
 export interface ClassExpectation {
   type: "class";
   parts: ClassParts;
@@ -47,7 +60,7 @@ export type Expectation =
   | LiteralExpectation
   | OtherExpectation;

-declare class _PeggySyntaxError extends Error {
+export declare class SyntaxError extends Error {
   /**
    * Constructs the human-readable message from the machine representation.
    *
@@ -55,21 +68,21 @@ declare class _PeggySyntaxError extends Error {
    * @param found Any text that will appear as found in the input instead of
    *   expected
    */
-  static buildMessage(expected: Expectation[], found: string | null): string;
-  message: string;
-  expected: Expectation[];
-  found: string | null;
-  location: LocationRange;
-  name: string;
+  static buildMessage(expected: Expectation[], found: string | null | undefined): string;
+  readonly message: string;
+  readonly expected: Expectation[];
+  readonly found: string | null | undefined;
+  readonly location: LocationRange;
+  readonly name: string;
   constructor(
     message: string,
     expected: Expectation[],
-    found: string | null,
+    found: string | null | undefined,
     location: LocationRange
   );
   format(
     sources: {
-      source?: any;
+      source?: Source | undefined;
       text: string;
     }[]
   ): string;
@@ -82,7 +95,8 @@ export interface ParserTracer {
 export type ParserTracerEvent =
   | { type: "rule.enter"; rule: string; location: LocationRange }
   | { type: "rule.fail"; rule: string; location: LocationRange }
-  | { type: "rule.match"; rule: string; result: any; location: LocationRange };
+  // `unknown` may be more appropriate but I looked at callsites and it seems like it's always a string or number
+  | { type: "rule.match"; rule: string; result: string | number; location: LocationRange };

 export type StartRules = $$$StartRules$$$;
 export interface ParseOptions<T extends StartRules = $$$DefaultStartRule$$$> {
@@ -91,24 +105,22 @@ export interface ParseOptions<T extends StartRules = $$$DefaultStartRule$$$> {
    * the parser. For example, this can be path to the parsed file or even the
    * File object.
    */
-  grammarSource?: any;
-  startRule?: T;
-  tracer?: ParserTracer;
+  grammarSource?: Source | undefined;
+  startRule?: T | undefined;
+  tracer?: ParserTracer | undefined;

   // Internal use only:
-  peg$library?: boolean;
+  peg$library?: boolean | undefined;
   // Internal use only:
-  peg$currPos?: number;
+  peg$currPos?: number | undefined;
   // Internal use only:
-  peg$silentFails?: number;
+  peg$silentFails?: number | undefined;
   // Internal use only:
-  peg$maxFailExpected?: Expectation[];
+  peg$maxFailExpected?: Expectation[] | undefined;
   // Extra application-specific properties
-  [key: string]: any;
+  [key: string]: unknown;
 }

 export declare const parse: typeof ParseFunction;
-export declare const SyntaxError: typeof _PeggySyntaxError;
-export type SyntaxError = _PeggySyntaxError;

 // Overload of ParseFunction for each allowedStartRule