Event handler for collapsible field expansion

[vxb1766]

Is there a callback for when a collapsible field is expanded?

Why do i need this? I am trying to modify dom nodes to reset the titles for collapsible fields(They are dynamic).
For eg: I need the expanded card field to say card1, card2 etc...
Since there is no solution for this yet, I tried doing it via dom Manipulation.

Array field template cannot achieve this as the Dom is still not available for .lead~.form-group > fieldset.