报错提示： "expires" directive is not allowed？

大神们，帮忙看个问题：
[code=plain]
server {
listen 80;
...
# expires 10s; //这句不报错
#下面这种写法，重启nginx会报错
if ($request_filename ~* ^.*?.(ico|jpeg|gif|jpg|png|woff)$){
expires 7d; //这句报错
}
...
}
[/code]
报错提示： "expires" directive is not allowed

https://www.jb51.net/article/64400.htm