<layout>
    <catalog_category_default>
        <!-- block gets added -->
        <reference name="content">
            <block type="core/text" name="are_you_sure"></block>
        </reference>
    </catalog_category_default>

    <catalog_category_default>
        <!-- later, a different handle gets a reference and sets block state -->
        <reference name="are_you_sure">
            <action method="setText"><text>Hello World</text></action>
        </reference>
    </catalog_category_default>

    <catalog_category_default>
        <!-- we want to move a block, so we unset where it is -->
        <reference name="content">
            <action method="unsetChild"><child>are_you_sure</child></action>
        </reference>
    </catalog_category_default>

    <catalog_category_default>
        <!-- WRONG WAY: we re-add the block, but we've lost state -->
        <reference name="right">
            <block type="core/text" name="are_you_sure"/>
        </reference>
    </catalog_category_default>

    <catalog_category_default>
        <!-- Instead, use the insert method.  This method accepts both a block object
        OR a string.  If you pass it a string, it gets a refernce to the block by that
        name.  The block, although unset, still exists on the layout object, which is why
        this works -->
        <reference name="right">
            <action method="insert"><block>are_you_sure</block></action>
        </reference>
        <!--
        if (is_string($block)) {
            $block = $this->getLayout()->getBlock($block);
        }
        -->
    </catalog_category_default>

</layout>