src/vs/workbench/contrib/terminal/browser/xterm/markNavigationAddon.ts/MarkNavigationAddon/_getOffset
class MarkNavigationAddon:	private _getOffset(xterm: Terminal): number {
		if (this._currentMarker === Boundary.Bottom) {
			return 0;
		} else if (this._currentMarker === Boundary.Top) {
			return 0 - (xterm.buffer.active.baseY + xterm.buffer.active.cursorY);
		} else {
			let offset = getLine(xterm, this._currentMarker);
			offset -= xterm.buffer.active.baseY + xterm.buffer.active.cursorY;
			return offset;
		}
	}