itemDescription not showing for HtmlSelectManyCheckbox

In JSF, I have an HtmlSelectManyCheckbox, defined like this:

<h:selectManyCheckbox required="true">
    <f:selectItem itemValue="0" itemLabel="cats" 
        itemDescription="Description not displayed"/>
    <f:selectItem itemValue="1" itemLabel="dogs"/>
    <f:selectItem itemValue="2" itemLabel="birds"/>
 ...

When the page 开发者_JAVA技巧is rendered, I can't see the itemDescription.

Is this a known behavior with JSF?

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From the Facelet Taglib Documentation:

itemLabel: Label to be displayed to the user for this option.

itemDescription: Description of this option, for use in development tools.

I understand this as the itemLabel is the displayed attribute.