> 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/4200-to-4206.md).

# Validation HTML Errors

Errors 4200 to 4206 are @aurelia/validation-html package related errors.

Please see below a reference to each [@aurelia/validation-html](https://github.com/aurelia/aurelia/tree/master/packages/validation-html) package related error with explanations and resources for debugging and solving.

## Validation HTML Errors (4200-4206)

These errors occur when using validation binding behaviors and validation controllers in HTML templates.

* [AUR4200](/developer-guides/error-messages/4200-to-4206/aur4200.md) - Validate binding behavior on invalid binding type
* [AUR4201](/developer-guides/error-messages/4200-to-4206/aur4201.md) - Validate binding behavior extraneous args
* [AUR4202](/developer-guides/error-messages/4200-to-4206/aur4202.md) - Validate binding behavior invalid trigger name
* [AUR4203](/developer-guides/error-messages/4200-to-4206/aur4203.md) - Validate binding behavior invalid controller
* [AUR4204](/developer-guides/error-messages/4200-to-4206/aur4204.md) - Validate binding behavior invalid binding target
* [AUR4205](/developer-guides/error-messages/4200-to-4206/aur4205.md) - Validation controller unknown expression
* [AUR4206](/developer-guides/error-messages/4200-to-4206/aur4206.md) - Validation controller unable to parse expression


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