# AUR0172

## Error Message

`AUR0172: Expression error: invalid tagged template on optional chain in "{{expression}}"`

## Description

This error occurs when a tagged template literal is used on an optional chain, which is not supported by Aurelia’s expression parser.

## Example Trigger

```html
<!-- ❌ Tagged template on optional chain -->
<div textcontent.bind="tag?.fn`x`"></div>
```

## Solution

* Avoid tagged templates in binding expressions. Move the logic into view-model code.