As petitioner is not in custody, denial of parental custody does not state a claim for Habeas relief under the statute.
https://www.ca10.uscourts.gov/opinions/18/18-5016.pdf
Since 2011. An occasional commonplacing of the U.S. Circuit Courts of Appeal.
Not written by a barrister. The name was thought up by a second-year American law student sitting in a coffeehouse in Manhattan. Neither an authoritative statement of the law nor legal advice.
Don't rely. Quick work.