Various fixes

- altIsMeta -> macOptionIsMeta
- Moved isThirdLevelShift into Terminal class
- Moved option check into isThirdLevelShift so it doesn't affect the Windows
  case and also includes the keypress case
- Add public API and typings test
- Add option checkbox to demo

src/Interfaces.ts

@@ -128,7 +128,6 @@ export interface IInputHandlingTerminal extends IEventEmitter {
 }
 
 export interface ITerminalOptions {
-  altIsMeta?: boolean;
   bellSound?: string;
   bellStyle?: string;
   cancelEvents?: boolean;
@@ -144,6 +143,7 @@ export interface ITerminalOptions {
   handler?: (data: string) => void;
   letterSpacing?: number;
   lineHeight?: number;
+  macOptionIsMeta?: boolean;
   rows?: number;
   screenKeys?: boolean;
   scrollback?: number;

src/Terminal.test.ts

@@ -523,10 +523,10 @@ describe('term.js addons', () => {
       });
     });
 
-    describe('with altIsMeta', () => {
+    describe('with macOptionIsMeta', () => {
       beforeEach(() => {
         term.browser.isMac = true;
-        term.setOption('altIsMeta', true);
+        term.setOption('macOptionIsMeta', true);
       });
       it('should return \\x1ba for alt+a', () => {
         assert.equal(term.evaluateKeyEscapeSequence({ altKey: true, keyCode: 65 }).key, '\x1ba');
@@ -613,10 +613,10 @@ describe('term.js addons', () => {
       };
     });
 
-    describe('with altIsMeta', () => {
+    describe('with macOptionIsMeta', () => {
       beforeEach(() => {
         term.browser.isMac = true;
-        term.setOption('altIsMeta', true);
+        term.setOption('macOptionIsMeta', true);
       });
 
       it('should interfere with the alt key on keyDown', () => {

src/Terminal.ts

@@ -80,7 +80,7 @@ const DEFAULT_OPTIONS: ITerminalOptions = {
   scrollback: 1000,
   screenKeys: false,
   debug: false,
-  altIsMeta: false,
+  macOptionIsMeta: false,
   cancelEvents: false,
   disableStdin: false,
   useFlowControl: false,
@@ -1375,7 +1375,7 @@ export class Terminal extends EventEmitter implements ITerminal, IInputHandlingT
       return this.cancel(ev, true);
     }
 
-    if (!this.options.altIsMeta && isThirdLevelShift(this.browser, ev)) {
+    if (this._isThirdLevelShift(this.browser, ev)) {
       return true;
     }
 
@@ -1396,6 +1396,19 @@ export class Terminal extends EventEmitter implements ITerminal, IInputHandlingT
     return this.cancel(ev, true);
   }
 
+  private _isThirdLevelShift(browser: IBrowser, ev: KeyboardEvent): boolean {
+    const thirdLevelKey =
+        (browser.isMac && !this.options.macOptionIsMeta && ev.altKey && !ev.ctrlKey && !ev.metaKey) ||
+        (browser.isMSWindows && ev.altKey && ev.ctrlKey && !ev.metaKey);
+
+    if (ev.type === 'keypress') {
+      return thirdLevelKey;
+    }
+
+    // Don't invoke for arrows, pageDown, home, backspace, etc. (on non-keypress events)
+    return thirdLevelKey && (!ev.keyCode || ev.keyCode > 47);
+  }
+
   /**
    * Returns an object that determines how a KeyboardEvent should be handled. The key of the
    * returned value is the new key code to pass to the PTY.
@@ -1700,8 +1713,8 @@ export class Terminal extends EventEmitter implements ITerminal, IInputHandlingT
             // ^] - Operating System Command (OSC)
             result.key = String.fromCharCode(29);
           }
-        } else if ((!this.browser.isMac || this.options.altIsMeta) && ev.altKey && !ev.ctrlKey && !ev.metaKey) {
-          // On Mac this is a third level shift. Use <Esc> instead if !altIsMeta
+        } else if ((!this.browser.isMac || this.options.macOptionIsMeta) && ev.altKey && !ev.ctrlKey && !ev.metaKey) {
+          // On macOS this is a third level shift when !macOptionIsMeta. Use <Esc> instead.
           if (ev.keyCode >= 65 && ev.keyCode <= 90) {
             result.key = C0.ESC + String.fromCharCode(ev.keyCode + 32);
           } else if (ev.keyCode === 192) {
@@ -1767,7 +1780,7 @@ export class Terminal extends EventEmitter implements ITerminal, IInputHandlingT
     }
 
     if (!key || (
-      (ev.altKey || ev.ctrlKey || ev.metaKey) && !isThirdLevelShift(this.browser, ev)
+      (ev.altKey || ev.ctrlKey || ev.metaKey) && !this._isThirdLevelShift(this.browser, ev)
     )) {
       return false;
     }
@@ -2159,19 +2172,6 @@ function off(el: any, type: string, handler: (event: Event) => any, capture: boo
   el.removeEventListener(type, handler, capture);
 }
 
-function isThirdLevelShift(browser: IBrowser, ev: KeyboardEvent): boolean {
-  const thirdLevelKey =
-      (browser.isMac && ev.altKey && !ev.ctrlKey && !ev.metaKey) ||
-      (browser.isMSWindows && ev.altKey && ev.ctrlKey && !ev.metaKey);
-
-  if (ev.type === 'keypress') {
-    return thirdLevelKey;
-  }
-
-  // Don't invoke for arrows, pageDown, home, backspace, etc. (on non-keypress events)
-  return thirdLevelKey && (!ev.keyCode || ev.keyCode > 47);
-}
-
 function wasMondifierKeyOnlyEvent(ev: KeyboardEvent): boolean {
   return ev.keyCode === 16 || // Shift
     ev.keyCode === 17 || // Ctrl