> For the complete documentation index, see [llms.txt](https://docs.aurelia.io/llms.txt). Markdown versions of documentation pages are available by appending `.md` to page URLs; this page is available as [Markdown](https://docs.aurelia.io/developer-guides/error-messages/0151-to-0179/aur0171.md).

# AUR0171

## Error Message

`AUR0171: Expression error: unexpected {{token}} at position "{{pos}}" for optional chain in "{{expression}}"`

## Description

This error occurs when optional chaining (`?.`, `?.[ ]`, etc.) is used in an unsupported or malformed way.

## Example Trigger

```html
<!-- ❌ Malformed optional chain -->
<div textcontent.bind="user?."></div>
```

## Solution

* Use valid optional chaining syntax, or use guards (`if.bind`) to avoid null access.

```html
<!-- ✅ -->
<div textcontent.bind="user?.name"></div>
```


---

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