How to reRender many components

I am using one rich:combobox(let say id="PARENT") and want to change dropdown list of two other rich:combobox(let say "CHILD1" and "CHILD2") according to selected attribute in first rich:combobox(PARENT).

How to do this ?

For changing only one rich:combobox(开发者_Python百科CHILD1 only), i used a4j:support(reRender) tag in "PARENT", but for two , i am not getting.

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The reRender attribute will take multiple ids separated by commas.

<a4j:support event="onchange" reRender="parent,child1,child2" />