将变量值转成小写字母。 等同于PHP的 strtolower()函数。
例子:
articleTitle:Two Convicts Evade Noose, Jury Hung.

模板:

_{$articleTitle}_
_{$articleTitle|lower}_

输出:

Two Convicts Evade Noose, Jury Hung.
two convicts evade noose, jury hung.