diff --git a/README.md b/README.md
index 57b0230..c3e8fda 100644
--- a/README.md
+++ b/README.md
@@ -5,3 +5,22 @@ Get the name of a number, even if it's stupidly big.
 ## References
 
 * [How high can you count?](http://www.isthe.com/chongo/tech/math/number/howhigh.html)
+
+## Features
+
+* Stringify/parse numbers and names in American/British short count (e.g. "million", "billion", "trillion"), or European
+  (e.g. "million", "milliard", "billion", "billiard", "trillion", "trilliard").
+* Support for exponential notation, even if in non-standard form (e.g. `123.45e+5`).
+* Support for negative numbers.
+
+See [TODO.md](TODO.md) for a list of features that are planned for implementation.
+
+## Limitations
+
+* Can only stringify and parse numbers and names that resolve to integer values.
+* Exponents `x` in values are limited to `Number.MAX_SAFE_INTEGER >~ x >~ Number.MIN_SAFE_INTEGER`.
+  Values may exceed extremes such as `Number.MAX_SAFE_INTEGER` and `Number.EPSILON` in which loss of
+  precision may occur.
+* No support for arbitrary number names such as "googol".
+* No support for fractional number names such as "half", "quarter", "third", "tenth", etc.
+* Supports only native types (`bigint`, `string`, `number`).
diff --git a/TODO.md b/TODO.md
index 1d0ae73..75356fa 100644
--- a/TODO.md
+++ b/TODO.md
@@ -1,3 +1,3 @@
 - [ ] Ordinals
-- [ ] Fractions
-- [ ] Other locales (long count, languages, etc.)
+- [ ] ~~Fractions~~
+- [X] Other locales (long count, languages, etc.)
diff --git a/packages/core/src/common.ts b/packages/core/src/common.ts
index b63edf1..af54815 100644
--- a/packages/core/src/common.ts
+++ b/packages/core/src/common.ts
@@ -1,7 +1,9 @@
+type Digit = '0' | '1' | '2' | '3' | '4' | '5' | '6' | '7' | '8' | '9';
+
 /**
  * Group digits.
  */
-type GroupDigits = string;
+export type GroupDigits = `${Digit}${Digit}${Digit}`;
 
 /**
  * Group place.
@@ -102,7 +104,7 @@ export interface NumberNameSystem {
 	 * Parses groups from a string.
 	 * @param tokens - The string to parse groups from.
 	 * @see {NumberNameSystem.stringifyGroups}
-	 * @returns Group[] The parsed groups.
+	 * @returns ParseResult The parsed groups as well as an indicator if the number is Boolean.
 	 */
 	parseGroups: (tokens: string[]) => ParseResult;
 	/**
@@ -115,6 +117,25 @@ export interface NumberNameSystem {
 	combineGroups: (groups: Group[], negative: boolean) => string;
 }
 
+/**
+ * Allowed value type for {@link stringify}.
+ */
+export type AllowedValue = string | number | bigint;
+
+/**
+ * Array of allowed types for {@link parse}.
+ */
+export const ALLOWED_PARSE_RESULT_TYPES = [
+	'string',
+	'number',
+	'bigint',
+] as const;
+
+/**
+ * Allowed type for {@link parse}.
+ */
+export type ParseResultType = typeof ALLOWED_PARSE_RESULT_TYPES[number];
+
 /**
  * Error thrown when an invalid token is encountered.
  */
@@ -124,6 +145,11 @@ export class InvalidTokenError extends Error {
 	}
 }
 
+/**
+ * Gets the maximum value from a list of bigints.
+ * @param b - The bigints to get the maximum value from.
+ * @returns bigint The maximum value.
+ */
 export const bigIntMax = (...b: bigint[]) => b.reduce(
 	(previousMax, current) => {
 		if (typeof previousMax === 'undefined') {
@@ -134,6 +160,11 @@ export const bigIntMax = (...b: bigint[]) => b.reduce(
 	undefined as bigint | undefined,
 );
 
+/**
+ * Gets the minimum value from a list of bigints.
+ * @param b - The bigints to get the minimum value from.
+ * @returns bigint The minimum value.
+ */
 export const bigIntMin = (...b: bigint[]) => b.reduce(
 	(previousMin, current) => {
 		if (typeof previousMin === 'undefined') {
diff --git a/packages/core/src/converter.ts b/packages/core/src/converter.ts
index e9e5dca..b1d9880 100644
--- a/packages/core/src/converter.ts
+++ b/packages/core/src/converter.ts
@@ -1,5 +1,10 @@
 import { enUS } from './systems';
-import { NumberNameSystem } from './common';
+import {
+	ALLOWED_PARSE_RESULT_TYPES,
+	AllowedValue,
+	NumberNameSystem,
+	ParseResultType,
+} from './common';
 import { exponentialToNumberString, extractExponentialComponents, numberToExponential } from './exponent';
 
 /**
@@ -12,25 +17,6 @@ const NEGATIVE_SYMBOL = '-' as const;
  */
 const EXPONENT_DELIMITER = 'e' as const;
 
-/**
- * Allowed value type for {@link stringify}.
- */
-export type AllowedValue = string | number | bigint;
-
-/**
- * Array of allowed types for {@link parse}.
- */
-const ALLOWED_PARSE_RESULT_TYPES = [
-	'string',
-	'number',
-	'bigint',
-] as const;
-
-/**
- * Allowed type for {@link parse}.
- */
-type ParseResult = typeof ALLOWED_PARSE_RESULT_TYPES[number];
-
 /**
  * Options to use when converting a value to a string.
  */
@@ -104,7 +90,7 @@ export interface ParseOptions {
 	/**
 	 * The type to parse the value as.
 	 */
-	type?: ParseResult;
+	type?: ParseResultType;
 }
 
 /**
@@ -115,7 +101,7 @@ export interface ParseOptions {
  */
 export const parse = (value: string, options = {} as ParseOptions) => {
 	const { system = enUS.shortCount, type: typeRaw = 'string' } = options;
-	const type = typeRaw.trim().toLowerCase() as ParseResult;
+	const type = typeRaw.trim().toLowerCase() as ParseResultType;
 
 	if (!((ALLOWED_PARSE_RESULT_TYPES as unknown as string[]).includes(type))) {
 		throw new TypeError(`Return type must be a string, number, or bigint. Received: ${type}`);
diff --git a/packages/core/src/exponent.ts b/packages/core/src/exponent.ts
index 0a625a1..0cf4bbd 100644
--- a/packages/core/src/exponent.ts
+++ b/packages/core/src/exponent.ts
@@ -1,7 +1,4 @@
-/**
- * Valid values that can be converted to exponential notation.
- */
-export type ValidValue = string | number | bigint;
+import { AllowedValue } from './common';
 
 interface BaseOptions {
 	/**
@@ -158,13 +155,13 @@ export const extractExponentialComponents = (
 };
 
 /**
- * Converts a numeric value to a string in exponential notation. Supports numbers of all types.
+ * Converts a numeric value to a string in exponential notation.
  * @param value - The value to convert.
  * @param options - Options to use when extracting components.
  * @returns string The value in exponential notation.
  */
 export const numberToExponential = (
-	value: ValidValue,
+	value: AllowedValue,
 	options = {} as NumberToExponentialOptions,
 ): string => {
 	const valueRaw = value as unknown;
@@ -216,6 +213,12 @@ export const numberToExponential = (
 	return `${significandInteger}${decimalPoint}${significandFractional}${exponentDelimiter}${exponent}`;
 };
 
+/**
+ * Converts a string in exponential notation (e.g. 1e+2) to a number string (e.g. 100).
+ * @param exp - The number in exponential notation to convert.
+ * @param options - Options to use when converting number strings.
+ * @returns string The number string.
+ */
 export const exponentialToNumberString = (
 	exp: string,
 	options = {} as ExponentialToNumberStringOptions,
diff --git a/packages/core/src/systems/en-UK/long-count/parse.ts b/packages/core/src/systems/en-UK/long-count/parse.ts
index 97f91be..585751d 100644
--- a/packages/core/src/systems/en-UK/long-count/parse.ts
+++ b/packages/core/src/systems/en-UK/long-count/parse.ts
@@ -2,7 +2,7 @@ import {
 	bigIntMax, bigIntMin,
 	Group,
 	GROUP_DIGITS_INDEX,
-	GROUP_PLACE_INDEX,
+	GROUP_PLACE_INDEX, GroupDigits,
 	InvalidTokenError,
 } from '../../../common';
 import {
@@ -269,14 +269,14 @@ const parseThousand = (acc: ParserState, token: string): ParserState => {
 	if (acc.mode === ParseGroupsMode.ONES_MODE) {
 		const ones = ONES.findIndex((o) => o === acc.lastToken);
 		if (ones > -1) {
-			lastGroup[GROUP_DIGITS_INDEX] = `${lastGroup[GROUP_DIGITS_INDEX].slice(0, 2)}${ones}`;
+			lastGroup[GROUP_DIGITS_INDEX] = `${lastGroup[GROUP_DIGITS_INDEX].slice(0, 2)}${ones}` as GroupDigits;
 		}
 	} else if (acc.mode === ParseGroupsMode.TENS_MODE) {
 		const tens = TENS.findIndex((t) => t === acc.lastToken);
 		if (tens > -1) {
 			lastGroup[GROUP_DIGITS_INDEX] = (
 				`${lastGroup[GROUP_DIGITS_INDEX].slice(0, 1)}${tens}${lastGroup[GROUP_DIGITS_INDEX].slice(2)}`
-			);
+			) as GroupDigits;
 		}
 	}
 
@@ -294,7 +294,7 @@ const parseThousand = (acc: ParserState, token: string): ParserState => {
 const parseHundred = (acc: ParserState): ParserState => {
 	const lastGroup = acc.groups.at(-1) ?? [...EMPTY_PLACE];
 	const hundreds = ONES.findIndex((o) => o === acc.lastToken);
-	lastGroup[GROUP_DIGITS_INDEX] = `${hundreds}${lastGroup[GROUP_DIGITS_INDEX].slice(1)}`;
+	lastGroup[GROUP_DIGITS_INDEX] = `${hundreds}${lastGroup[GROUP_DIGITS_INDEX].slice(1)}` as GroupDigits;
 	return {
 		...acc,
 		groups: [...acc.groups.slice(0, -1), lastGroup],
@@ -308,7 +308,7 @@ const parseFinal = (acc: ParserState): ParserState => {
 	if (acc.mode === ParseGroupsMode.ONES_MODE) {
 		const ones = ONES.findIndex((o) => o === acc.lastToken);
 		if (ones > -1) {
-			lastGroup[GROUP_DIGITS_INDEX] = `${lastGroup[GROUP_DIGITS_INDEX].slice(0, 2)}${ones}`;
+			lastGroup[GROUP_DIGITS_INDEX] = `${lastGroup[GROUP_DIGITS_INDEX].slice(0, 2)}${ones}` as GroupDigits;
 		}
 		// We assume last token without parsed place will always be the smallest
 		lastGroup[GROUP_PLACE_INDEX] = BigInt(0);
@@ -322,7 +322,9 @@ const parseFinal = (acc: ParserState): ParserState => {
 	if (acc.mode === ParseGroupsMode.TENS_MODE) {
 		const tens = TENS.findIndex((o) => o === acc.lastToken);
 		if (tens > -1) {
-			lastGroup[GROUP_DIGITS_INDEX] = `${lastGroup[0].slice(0, 1)}${tens}${lastGroup[GROUP_DIGITS_INDEX].slice(2)}`;
+			lastGroup[GROUP_DIGITS_INDEX] = (
+				`${lastGroup[0].slice(0, 1)}${tens}${lastGroup[GROUP_DIGITS_INDEX].slice(2)}`
+			) as GroupDigits;
 		}
 		lastGroup[GROUP_PLACE_INDEX] = BigInt(0);
 		return {
@@ -360,11 +362,11 @@ const parseTenPlusOnes = (acc: ParserState, token: string): ParserState => {
 			...acc,
 			lastToken: token,
 			mode: ParseGroupsMode.TEN_PLUS_ONES_MODE,
-			groups: [...acc.groups, [`01${tenPlusOnes}`, lastGroup[GROUP_PLACE_INDEX] - BigInt(1)]],
+			groups: [...acc.groups, [`01${tenPlusOnes}` as GroupDigits, lastGroup[GROUP_PLACE_INDEX] - BigInt(1)]],
 		};
 	}
 
-	lastGroup[GROUP_DIGITS_INDEX] = `${lastGroup[GROUP_DIGITS_INDEX].slice(0, 1)}1${tenPlusOnes}`;
+	lastGroup[GROUP_DIGITS_INDEX] = `${lastGroup[GROUP_DIGITS_INDEX].slice(0, 1)}1${tenPlusOnes}` as GroupDigits;
 	return {
 		...acc,
 		lastToken: token,
@@ -381,13 +383,14 @@ const parseTens = (acc: ParserState, token: string): ParserState => {
 			...acc,
 			lastToken: token,
 			mode: ParseGroupsMode.TENS_MODE,
-			groups: [...acc.groups, [`0${tens}0`, lastGroup[GROUP_PLACE_INDEX] - BigInt(1)]],
+			groups: [...acc.groups, [`0${tens}0` as GroupDigits, lastGroup[GROUP_PLACE_INDEX] - BigInt(1)]],
 		};
 	}
 
 	lastGroup[GROUP_DIGITS_INDEX] = (
 		`${lastGroup[GROUP_DIGITS_INDEX].slice(0, 1)}${tens}${lastGroup[GROUP_DIGITS_INDEX].slice(2)}`
-	);
+	) as GroupDigits;
+
 	return {
 		...acc,
 		lastToken: token,
diff --git a/packages/core/src/systems/en-UK/long-count/stringify.ts b/packages/core/src/systems/en-UK/long-count/stringify.ts
index 96928af..a6432f0 100644
--- a/packages/core/src/systems/en-UK/long-count/stringify.ts
+++ b/packages/core/src/systems/en-UK/long-count/stringify.ts
@@ -1,7 +1,7 @@
 import {
 	Group,
 	GROUP_DIGITS_INDEX,
-	GROUP_PLACE_INDEX,
+	GROUP_PLACE_INDEX, GroupDigits,
 	GroupPlace,
 } from '../../../common';
 import { numberToExponential } from '../../../exponent';
@@ -179,16 +179,16 @@ const getGroupName = (place: GroupPlace, shortenMillia: boolean) => {
 				const currentPlace = BigInt(Math.floor((cc.length - i - 1) / 3));
 				const newGroup = [EMPTY_GROUP_DIGITS, currentPlace] as Group;
 				if (typeof firstGroup === 'undefined') {
-					newGroup[GROUP_DIGITS_INDEX] = c;
+					newGroup[GROUP_DIGITS_INDEX] = c as GroupDigits;
 					return [newGroup];
 				}
 
 				if (firstGroup[0].length > 2) {
-					newGroup[GROUP_DIGITS_INDEX] = c;
+					newGroup[GROUP_DIGITS_INDEX] = c as GroupDigits;
 					return [newGroup, ...acc];
 				}
 
-				newGroup[GROUP_DIGITS_INDEX] = c + firstGroup[0];
+				newGroup[GROUP_DIGITS_INDEX] = (c + firstGroup[0]) as GroupDigits;
 				return [
 					newGroup,
 					...acc.slice(1),
@@ -309,11 +309,11 @@ export const splitIntoGroups = (value: string): Group[] => {
 				const lastGroupDigits = lastGroup[0].split('');
 				lastGroupDigits[currentPlaceInGroup] = c;
 				return [...acc.slice(0, -1) ?? [], [
-					lastGroupDigits.join(''),
+					lastGroupDigits.join('') as GroupDigits,
 					currentPlace,
 				]];
 			}
-			return [...acc, [c.padEnd(3, '0'), currentPlace]];
+			return [...acc, [c.padEnd(3, '0') as GroupDigits, currentPlace]];
 		},
 		[],
 	);
diff --git a/packages/core/src/systems/en-US/short-count/parse.ts b/packages/core/src/systems/en-US/short-count/parse.ts
index aaf56bf..e76c04f 100644
--- a/packages/core/src/systems/en-US/short-count/parse.ts
+++ b/packages/core/src/systems/en-US/short-count/parse.ts
@@ -2,7 +2,7 @@ import {
 	bigIntMax, bigIntMin,
 	Group,
 	GROUP_DIGITS_INDEX,
-	GROUP_PLACE_INDEX,
+	GROUP_PLACE_INDEX, GroupDigits,
 	InvalidTokenError,
 } from '../../../common';
 import {
@@ -267,14 +267,14 @@ const parseThousand = (acc: ParserState, token: string): ParserState => {
 	if (acc.mode === ParseGroupsMode.ONES_MODE) {
 		const ones = ONES.findIndex((o) => o === acc.lastToken);
 		if (ones > -1) {
-			lastGroup[GROUP_DIGITS_INDEX] = `${lastGroup[GROUP_DIGITS_INDEX].slice(0, 2)}${ones}`;
+			lastGroup[GROUP_DIGITS_INDEX] = `${lastGroup[GROUP_DIGITS_INDEX].slice(0, 2)}${ones}` as GroupDigits;
 		}
 	} else if (acc.mode === ParseGroupsMode.TENS_MODE) {
 		const tens = TENS.findIndex((t) => t === acc.lastToken);
 		if (tens > -1) {
 			lastGroup[GROUP_DIGITS_INDEX] = (
 				`${lastGroup[GROUP_DIGITS_INDEX].slice(0, 1)}${tens}${lastGroup[GROUP_DIGITS_INDEX].slice(2)}`
-			);
+			) as GroupDigits;
 		}
 	}
 
@@ -292,7 +292,7 @@ const parseThousand = (acc: ParserState, token: string): ParserState => {
 const parseHundred = (acc: ParserState): ParserState => {
 	const lastGroup = acc.groups.at(-1) ?? [...EMPTY_PLACE];
 	const hundreds = ONES.findIndex((o) => o === acc.lastToken);
-	lastGroup[GROUP_DIGITS_INDEX] = `${hundreds}${lastGroup[GROUP_DIGITS_INDEX].slice(1)}`;
+	lastGroup[GROUP_DIGITS_INDEX] = `${hundreds}${lastGroup[GROUP_DIGITS_INDEX].slice(1)}` as GroupDigits;
 	return {
 		...acc,
 		groups: [...acc.groups.slice(0, -1), lastGroup],
@@ -306,7 +306,7 @@ const parseFinal = (acc: ParserState): ParserState => {
 	if (acc.mode === ParseGroupsMode.ONES_MODE) {
 		const ones = ONES.findIndex((o) => o === acc.lastToken);
 		if (ones > -1) {
-			lastGroup[GROUP_DIGITS_INDEX] = `${lastGroup[GROUP_DIGITS_INDEX].slice(0, 2)}${ones}`;
+			lastGroup[GROUP_DIGITS_INDEX] = `${lastGroup[GROUP_DIGITS_INDEX].slice(0, 2)}${ones}` as GroupDigits;
 		}
 		// We assume last token without parsed place will always be the smallest
 		lastGroup[GROUP_PLACE_INDEX] = BigInt(0);
@@ -320,7 +320,9 @@ const parseFinal = (acc: ParserState): ParserState => {
 	if (acc.mode === ParseGroupsMode.TENS_MODE) {
 		const tens = TENS.findIndex((o) => o === acc.lastToken);
 		if (tens > -1) {
-			lastGroup[GROUP_DIGITS_INDEX] = `${lastGroup[0].slice(0, 1)}${tens}${lastGroup[GROUP_DIGITS_INDEX].slice(2)}`;
+			lastGroup[GROUP_DIGITS_INDEX] = (
+				`${lastGroup[0].slice(0, 1)}${tens}${lastGroup[GROUP_DIGITS_INDEX].slice(2)}`
+			) as GroupDigits;
 		}
 		lastGroup[GROUP_PLACE_INDEX] = BigInt(0);
 		return {
@@ -358,11 +360,11 @@ const parseTenPlusOnes = (acc: ParserState, token: string): ParserState => {
 			...acc,
 			lastToken: token,
 			mode: ParseGroupsMode.TEN_PLUS_ONES_MODE,
-			groups: [...acc.groups, [`01${tenPlusOnes}`, lastGroup[GROUP_PLACE_INDEX] - BigInt(1)]],
+			groups: [...acc.groups, [`01${tenPlusOnes}` as GroupDigits, lastGroup[GROUP_PLACE_INDEX] - BigInt(1)]],
 		};
 	}
 
-	lastGroup[GROUP_DIGITS_INDEX] = `${lastGroup[GROUP_DIGITS_INDEX].slice(0, 1)}1${tenPlusOnes}`;
+	lastGroup[GROUP_DIGITS_INDEX] = `${lastGroup[GROUP_DIGITS_INDEX].slice(0, 1)}1${tenPlusOnes}` as GroupDigits;
 	return {
 		...acc,
 		lastToken: token,
@@ -379,13 +381,14 @@ const parseTens = (acc: ParserState, token: string): ParserState => {
 			...acc,
 			lastToken: token,
 			mode: ParseGroupsMode.TENS_MODE,
-			groups: [...acc.groups, [`0${tens}0`, lastGroup[GROUP_PLACE_INDEX] - BigInt(1)]],
+			groups: [...acc.groups, [`0${tens}0` as GroupDigits, lastGroup[GROUP_PLACE_INDEX] - BigInt(1)]],
 		};
 	}
 
 	lastGroup[GROUP_DIGITS_INDEX] = (
 		`${lastGroup[GROUP_DIGITS_INDEX].slice(0, 1)}${tens}${lastGroup[GROUP_DIGITS_INDEX].slice(2)}`
-	);
+	) as GroupDigits;
+
 	return {
 		...acc,
 		lastToken: token,
diff --git a/packages/core/src/systems/en-US/short-count/stringify.ts b/packages/core/src/systems/en-US/short-count/stringify.ts
index 86c8390..3b0d8c3 100644
--- a/packages/core/src/systems/en-US/short-count/stringify.ts
+++ b/packages/core/src/systems/en-US/short-count/stringify.ts
@@ -1,7 +1,7 @@
 import {
 	Group,
 	GROUP_DIGITS_INDEX,
-	GROUP_PLACE_INDEX,
+	GROUP_PLACE_INDEX, GroupDigits,
 	GroupPlace,
 } from '../../../common';
 import { numberToExponential } from '../../../exponent';
@@ -177,16 +177,16 @@ const getGroupName = (place: GroupPlace, shortenMillia: boolean) => {
 				const currentPlace = BigInt(Math.floor((cc.length - i - 1) / 3));
 				const newGroup = [EMPTY_GROUP_DIGITS, currentPlace] as Group;
 				if (typeof firstGroup === 'undefined') {
-					newGroup[GROUP_DIGITS_INDEX] = c;
+					newGroup[GROUP_DIGITS_INDEX] = c as GroupDigits;
 					return [newGroup];
 				}
 
 				if (firstGroup[0].length > 2) {
-					newGroup[GROUP_DIGITS_INDEX] = c;
+					newGroup[GROUP_DIGITS_INDEX] = c as GroupDigits;
 					return [newGroup, ...acc];
 				}
 
-				newGroup[GROUP_DIGITS_INDEX] = c + firstGroup[0];
+				newGroup[GROUP_DIGITS_INDEX] = (c + firstGroup[0]) as GroupDigits;
 				return [
 					newGroup,
 					...acc.slice(1),
@@ -307,11 +307,11 @@ export const splitIntoGroups = (value: string): Group[] => {
 				const lastGroupDigits = lastGroup[0].split('');
 				lastGroupDigits[currentPlaceInGroup] = c;
 				return [...acc.slice(0, -1), [
-					lastGroupDigits.join(''),
+					lastGroupDigits.join('') as GroupDigits,
 					currentPlace,
 				]];
 			}
-			return [...acc, [c.padEnd(3, '0'), currentPlace]];
+			return [...acc, [c.padEnd(3, '0') as GroupDigits, currentPlace]];
 		},
 		[],
 	);