Custom Plugin - how to update the rich-combo label, regarding to the current selection

Hello!

I'm developing a plugin for CKEditor4 and my work is based on a richCombo control.

The user can choose an entry from the combo and the selected entry is used to change something inside of the current selection. I'm updating the current label of the control by setting it's value (setValue).

My question is, how can I update the label of the control if the user clicks somewhere in the text?
I'm meaning the "way back" from the current selection into the richCombo control.

A similar example : 
If a text was set to "bold" and you select this text, then the bold-button is automatically displayed as selected.

How can I achieve this behavior with my custom richCombo?

Thanks

mala