Custom code to be executed when step is moved in sequence

[bigyo]

Hello All,

I'm using a customized SequenceEditor GUI in my project.

I would like create a custom code module, which would run when the step is moved in the sequence, so the position of the step is changed.

Can I trigger somehow to that? 

How could I get the value change of the Step.StepIndex?

Or is there any UImessage which could be used?

Thank you in advance.