# 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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# Agent Instructions: Querying This Documentation

If you need additional information that is not directly available in this page, you can query the documentation dynamically by asking a question.

Perform an HTTP GET request on the current page URL with the `ask` query parameter:

```
GET https://docs.aurelia.io/developer-guides/error-messages/0151-to-0179/aur0171.md?ask=<question>
```

The question should be specific, self-contained, and written in natural language.
The response will contain a direct answer to the question and relevant excerpts and sources from the documentation.

Use this mechanism when the answer is not explicitly present in the current page, you need clarification or additional context, or you want to retrieve related documentation sections.