The article incorporates public domain text from the reference.

But if we're talking a bunch of public domain texts or unknown authors?

The original version of this article is from the public domain text at this site.

This article incorporates public domain text created by the US government.

Portions of this article are based on public domain text from the White House.

This article incorporates public domain text from the United States government.

This article contains public domain text created by the United States government.

Public domain text used as source for this article.

Portions of this article are based on public domain text from ibiblio.

This article used public domain text from the Voice of America, as identified.