Unknown PerlIO layer class ':utf8 :std'

Question

Doc states that expressions are equivalent:

use open ':locale';
use open IO => ':locale';

But why next are not?

use open ':utf8 :std';       # Unknown PerlIO layer class ':utf8 :std' (need IN, OUT or IO) at ...
use open IO => ':utf8 :std'; # No error happened

Answer 1

Thank @Grinnz on IRC:

Because :std is not a layer, it must be its own argument in the list

So code should be:

use open ':utf8', ':std';