smarty内置函数capture用法分析

{capture name="banner"}aaaaaa{/capture}
{$smarty.capture.banner}
<hr />
{capture assign="foo"}bbbbbb{/capture}
{$foo}
<hr />
{capture append="arr"}hello{/capture}
{capture append="arr"}world{/capture}
{foreach $arr as $value}
{$value}
{/foreach}