diff --git a/src/common/all_test.ts b/src/common/all_test.ts
index 57e98c1..7bb82a4 100644
--- a/src/common/all_test.ts
+++ b/src/common/all_test.ts
@@ -307,6 +307,14 @@ testSuite({
 			assertFalse(isAscii('😺acalskjsdf'));
 			assertFalse(isAscii('ab😺ac'));
 		},
+		'isAsciiDigit()': () => {
+			const { isAsciiDigit } = Fn;
+
+			assertTrue(isAsciiDigit('1234567890'));
+			assertFalse(isAsciiDigit('A1'));
+			assertFalse(isAsciiDigit('/'));
+			assertFalse(isAsciiDigit(':'));
+		},
 		'isControl()': () => {
 			const { isControl } = Fn;
 
diff --git a/src/common/ansi.ts b/src/common/ansi.ts
index 05386f0..af0d838 100644
--- a/src/common/ansi.ts
+++ b/src/common/ansi.ts
@@ -106,6 +106,7 @@ const moveCursorForward = (col: number): string => code(col, 'C');
 const moveCursorDown = (row: number): string => code(row, 'B');
 const textFormat = (param: string | number | string[] | number[]): string =>
 	code(param, 'm');
+const color = (value: AnsiColor): string => textFormat(value);
 const color256 = (value: number, ground: Ground = Ground.Fore): string =>
 	textFormat([ground, AnsiColor.Type256, value]);
 const rgb = (
@@ -128,6 +129,7 @@ export const Ansi = {
 	moveCursorForward,
 	moveCursorDown,
 	textFormat,
+	color,
 	color256,
 	rgb,
 };
diff --git a/src/common/document.ts b/src/common/document.ts
index e6ac5bb..1e92e05 100644
--- a/src/common/document.ts
+++ b/src/common/document.ts
@@ -72,6 +72,9 @@ export class Document {
 		return this.#rows.length === 0;
 	}
 
+	/**
+	 * Open a file for editing
+	 */
 	public async open(filename: string): Promise<Document> {
 		const { file } = await getRuntime();
 
@@ -89,6 +92,9 @@ export class Document {
 		return this;
 	}
 
+	/**
+	 * Save the current document
+	 */
 	public async save(filename: string) {
 		const { file } = await getRuntime();
 
@@ -149,6 +155,10 @@ export class Document {
 		this.dirty = true;
 	}
 
+	/**
+	 * Remove a character from the document, merging
+	 * adjacent lines if necessary
+	 */
 	public delete(at: Position): void {
 		const len = this.numRows;
 		if (at.y >= len) {
diff --git a/src/common/fns.ts b/src/common/fns.ts
index 75153d9..3180abc 100644
--- a/src/common/fns.ts
+++ b/src/common/fns.ts
@@ -159,6 +159,16 @@ export function isAscii(char: string): boolean {
 	return strChars(char).every((char) => ord(char) < 0x80);
 }
 
+/**
+ * Are all the characters numerals?
+ *
+ * @param char - string to check
+ */
+export function isAsciiDigit(char: string): boolean {
+	return isAscii(char) &&
+		strChars(char).every((char) => ord(char) >= 0x30 && ord(char) < 0x3a);
+}
+
 /**
  * Is the one char in the string an ascii control character?
  *
diff --git a/src/common/row.ts b/src/common/row.ts
index 322ef9b..8575e77 100644
--- a/src/common/row.ts
+++ b/src/common/row.ts
@@ -16,6 +16,11 @@ export class Row {
 	 */
 	render: string[] = [];
 
+	/**
+	 * The syntax highlighting map
+	 */
+	hl: string[] = [];
+
 	private constructor(s: string | string[] = '') {
 		this.chars = Array.isArray(s) ? s : strChars(s);
 		this.render = [];
diff --git a/src/common/types.ts b/src/common/types.ts
index 271a26c..7745468 100644
--- a/src/common/types.ts
+++ b/src/common/types.ts
@@ -162,6 +162,11 @@ export enum SearchDirection {
 	Backward = -1,
 }
 
+export enum HighlightType {
+	None,
+	Number,
+}
+
 // ----------------------------------------------------------------------------
 // Testing
 // ----------------------------------------------------------------------------