page.xml 定义：
----------------------------
<block type="core/text_list" name="right" as="right" translate="label">
<label>Right Column</label>
</block>
=============================================
在catalog.xml里用reference 来扩展定义：
首页右边栏：
-------------------------------------
<default>
<reference name="right">
<block type="catalog/product_compare_sidebar" before="cart_sidebar" name="catalog.compare.sidebar" template="catalog/product/compare/sidebar.phtml"/>
<block type="core/template" name="right.permanent.callout" template="callouts/right_col.phtml">
<action method="setImgSrc"><src>p_w_picpaths/media/col_right_callout.jpg</src></action>
<action method="setImgAlt" translate="alt" module="catalog"><alt>Keep your eyes open for our special Back to School items and save A LOT!</alt></action>
</block>
</reference>
</default>
============================================
具体商品详细页：
-------------------------------------
<!--
Product view
-->
<catalog_product_view translate="label">
<label>Catalog Product View (Any)</label>
<reference name="right">
<block type="catalog/product_list_related" name="catalog.product.related" before="-" template="catalog/product/list/related.phtml"/>
</reference>
</catalog_product_view>
==========================================
用before,after 选择器来决定区块的位置，before="-"表示位于最前面。
