> 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/aur0172.md).

# 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.


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