diff --git a/src/vs/base/common/htmlContent.ts b/src/vs/base/common/htmlContent.ts
index 9e8a13a3a39375ed779e8a922ecd9fa8d13bef0a..663274bc6927aac0a2d6aa2bf0c9adba9a69ca0a 100644
--- a/src/vs/base/common/htmlContent.ts
+++ b/src/vs/base/common/htmlContent.ts
@@ -16,52 +16,52 @@ export interface IMarkdownString {
 }
 
 export class MarkdownString implements IMarkdownString {
-	private readonly _isTrusted: boolean;
-	private readonly _supportThemeIcons: boolean;
+
+	public value: string;
+	public isTrusted?: boolean;
+	public supportThemeIcons?: boolean;
 
 	constructor(
-		private _value: string = '',
+		value: string = '',
 		isTrustedOrOptions: boolean | { isTrusted?: boolean, supportThemeIcons?: boolean } = false,
 	) {
-		if (typeof this._value !== 'string') {
+		this.value = value;
+		if (typeof this.value !== 'string') {
 			throw illegalArgument('value');
 		}
 
 		if (typeof isTrustedOrOptions === 'boolean') {
-			this._isTrusted = isTrustedOrOptions;
-			this._supportThemeIcons = false;
+			this.isTrusted = isTrustedOrOptions;
+			this.supportThemeIcons = false;
 		}
 		else {
-			this._isTrusted = isTrustedOrOptions.isTrusted ?? false;
-			this._supportThemeIcons = isTrustedOrOptions.supportThemeIcons ?? false;
+			this.isTrusted = isTrustedOrOptions.isTrusted ?? false;
+			this.supportThemeIcons = isTrustedOrOptions.supportThemeIcons ?? false;
 		}
 	}
 
-	get value() { return this._value; }
-	get isTrusted() { return this._isTrusted; }
-	get supportThemeIcons() { return this._supportThemeIcons; }
-
 	appendText(value: string): MarkdownString {
 		// escape markdown syntax tokens: http://daringfireball.net/projects/markdown/syntax#backslash
-		this._value += (this._supportThemeIcons ? escapeCodicons(value) : value)
+		this.value += (this.supportThemeIcons ? escapeCodicons(value) : value)
 			.replace(/[\\`*_{}[\]()#+\-.!]/g, '\\$&')
+			.replace(/^([ \t]+)(.+)$/gm, (_match, g1, g2) => ' '.repeat(g1.length) + g2)
+			.replace(/^>/gm, '\\>')
 			.replace(/\n/g, '\n\n');
 
 		return this;
 	}
 
 	appendMarkdown(value: string): MarkdownString {
-		this._value += value;
-
+		this.value += value;
 		return this;
 	}
 
 	appendCodeblock(langId: string, code: string): MarkdownString {
-		this._value += '\n```';
-		this._value += langId;
-		this._value += '\n';
-		this._value += code;
-		this._value += '\n```\n';
+		this.value += '\n```';
+		this.value += langId;
+		this.value += '\n';
+		this.value += code;
+		this.value += '\n```\n';
 		return this;
 	}
 }
diff --git a/src/vs/base/test/common/markdownString.test.ts b/src/vs/base/test/common/markdownString.test.ts
index f33f741f624ad6e118f90666541746d032424ff5..a76c30f2cc57c2fc4aca485760943fb57da03851 100644
--- a/src/vs/base/test/common/markdownString.test.ts
+++ b/src/vs/base/test/common/markdownString.test.ts
@@ -8,6 +8,18 @@ import { MarkdownString } from 'vs/base/common/htmlContent';
 
 suite('MarkdownString', () => {
 
+	test('Escape leading whitespace', function () {
+		const mds = new MarkdownString();
+		mds.appendText('Hello\n    Not a code block');
+		assert.equal(mds.value, 'Hello\n\n    Not a code block');
+	});
+
+	test('MarkdownString.appendText doesn\'t escape quote #109040', function () {
+		const mds = new MarkdownString();
+		mds.appendText('> Text\n>More');
+		assert.equal(mds.value, '\\> Text\n\n\\>More');
+	});
+
 	test('appendText', () => {
 
 		const mds = new MarkdownString();
diff --git a/src/vs/workbench/api/common/extHostTypes.ts b/src/vs/workbench/api/common/extHostTypes.ts
index 6eb858eee8415a6fb521bf3e8c0ad514e2c4834e..158eb96407d36bf7a9bc44112b33396203fbeac1 100644
--- a/src/vs/workbench/api/common/extHostTypes.ts
+++ b/src/vs/workbench/api/common/extHostTypes.ts
@@ -4,10 +4,9 @@
  *--------------------------------------------------------------------------------------------*/
 
 import { coalesceInPlace, equals } from 'vs/base/common/arrays';
-import { escapeCodicons } from 'vs/base/common/codicons';
 import { illegalArgument } from 'vs/base/common/errors';
 import { IRelativePattern } from 'vs/base/common/glob';
-import { isMarkdownString } from 'vs/base/common/htmlContent';
+import { isMarkdownString, MarkdownString as BaseMarkdownString } from 'vs/base/common/htmlContent';
 import { ResourceMap } from 'vs/base/common/map';
 import { isStringArray } from 'vs/base/common/types';
 import { URI } from 'vs/base/common/uri';
@@ -1290,40 +1289,7 @@ export class CodeInset {
 
 
 @es5ClassCompat
-export class MarkdownString {
-
-	value: string;
-	isTrusted?: boolean;
-	readonly supportThemeIcons?: boolean;
-
-	constructor(value?: string, supportThemeIcons: boolean = false) {
-		this.value = value ?? '';
-		this.supportThemeIcons = supportThemeIcons;
-	}
-
-	appendText(value: string): MarkdownString {
-		// escape markdown syntax tokens: http://daringfireball.net/projects/markdown/syntax#backslash
-		this.value += (this.supportThemeIcons ? escapeCodicons(value) : value)
-			.replace(/[\\`*_{}[\]()#+\-.!]/g, '\\$&')
-			.replace(/\n/, '\n\n');
-
-		return this;
-	}
-
-	appendMarkdown(value: string): MarkdownString {
-		this.value += value;
-
-		return this;
-	}
-
-	appendCodeblock(code: string, language: string = ''): MarkdownString {
-		this.value += '\n```';
-		this.value += language;
-		this.value += '\n';
-		this.value += code;
-		this.value += '\n```\n';
-		return this;
-	}
+export class MarkdownString extends BaseMarkdownString implements vscode.MarkdownString {
 
 	static isMarkdownString(thing: any): thing is vscode.MarkdownString {
 		if (thing instanceof MarkdownString) {
@@ -1331,6 +1297,11 @@ export class MarkdownString {
 		}
 		return thing && thing.appendCodeblock && thing.appendMarkdown && thing.appendText && (thing.value !== undefined);
 	}
+
+	constructor(value?: string, supportThemeIcons: boolean = false) {
+		super(value ?? '', { supportThemeIcons });
+	}
+
 }
 
 @es5ClassCompat