smarty?截取字符串,该如何解决

smarty?截取字符串

<{section name=s loop=$eventinfo}>
<{$eventinfo[s].start_mm}>  (October )
//怎么获取$eventinfo[s].start_mm 的前三个字母 (Oct)
<{/section}>

------解决思路----------------------
<{$eventinfo[s].start_mm
------解决思路----------------------
substr:0:3}>