Improve indication of strict validation mode

[nikku]

Is your feature request related to a problem? Please describe

As I edit properties in the panel elements get validated in strict or lax mode. In strict validation mode we don't serialize critical properties (ID) thus maintaining the integrity of the underlying model.

Unfortunately we don't indicate to the user that the contents of the element are not accepted, leading to unpleasant surprises. As a user I cannot distinguish strict and lax mode.

Describe the solution you'd like

• Restore valid in strict mode immediately after the element is blurred.

Describe alternatives you've considered

Add additional, visual indication to distinguish strict from lax validation mode.

Additional context

This issue was previously user reported, it is especially confusing in the context of element templates, where strict validation is currently applies (when it should not).

[nikku]

@pinussilvestrus do you have context why we decided to implement it this way (don't restore on blur)?

[pinussilvestrus]

As far as I can remember we simply re-used the same validation approach as in the 0.x properties panel.
: bpmn-io/properties-panel#27

[nikku]

Thanks @pinussilvestrus. That helps a lot. The referenced issue explicitly states:

[...] the last valid input value should be restored.

(Without mentioning when the restoration shall happen, which is crucial 🙈).