AUR4205

Error Message

AUR4205: Unknown expression of type {{type}}

Where {{type}} is the runtime expression type encountered by the validation controller.

Description

This error occurs when the validation controller encounters a binding/expression shape that it does not understand or cannot work with. This typically happens when using validation with an unsupported binding expression type or a custom/extended expression that the controller cannot interpret.

Common Scenarios

• Using validation APIs against a binding that is not a standard property binding.

• Custom expression transforms/plugins that produce expression nodes the validation controller does not recognize.

Solution

• Use validation with standard property bindings, or validate programmatically using a supported API.

• If you are extending expression parsing/compilation, ensure your extensions are compatible with validation-html.

Troubleshooting

• Capture/log the expression type shown in {{type}} and locate where it originates.

• Reduce the binding to a simple value.bind/checked.bind and re-introduce complexity to find the incompatible part.