https://sourceforge.net/tracker/?func=detail&aid=3286348&group_id=152762&atid=785194

For example,

<combobutton label="IfAny" onClick="" onOpen="" >
<combopopup>
// any component set
</combopopup>
</combobutton>

As the attached image file, the combobutton should support onClick event when user click upon the left of the button and onOpen when user click upon the right-most of the button (like arrow icon).