Art. 11.01. WHAT WRIT IS.  The writ of habeas corpus is the remedy to be used when any person is restrained in his liberty.  It is an order issued by a court or judge of competent jurisdiction, directed to any one having a person in his custody, or under his restraint, commanding him to produce such person, at a time and place named in the writ, and show why he is held in custody or under restraint.
Acts 1965, 59th Leg., vol. 2, p. 317, ch. 722.