Texas Penal Code - PENAL § 39.01. Definitions

(A) imposes a duty on the public servant;  or

(B) governs the conduct of the public servant.

(A) an agreement under which the public servant holds the property;

(B) a contract of employment or oath of office of a public servant;

(C) a law, including provisions of the General Appropriations Act specifically relating to government property, that prescribes the manner of custody or disposition of the property;  or

(D) a limited purpose for which the property is delivered or received.