The "American Rescue Plan" was passed as law and provided for advanced payment of Child Tax Credits. Normally, an overpayment would have to be returned to the IRS, but the law provides a "Safe Harbor" for certain income groups, allowing them to keep credit sent in excess.
The IRS website says that this Safe Harbor (they call it Repayment Protection) may be limited for people living outside the U.S. for more than half a year, but does not clarify what the qualifier "may" means. This information is mirrored on many tax preparation websites.
Where in the text of the law (linked above) is such a limitation mentioned, and why may it be/not be applied?