Md. Code, Real Prop. § 2-126

(a) (1) In this section the following words have the meanings indicated. (2) “Accessory dwelling unit” has the meaning stated in § 4–501 of the Land Use Article. (3) “Restriction on use” includes any covenant, restriction, or condition contained in: (i) A deed; (ii) A declaration; (iii) A contract; (iv) The bylaws or rules of a homeowners association; (v) A security instrument; or (vi) Any other instrument affecting: 1. The transfer or sale of real property; or 2. Any other interest in real property. (b) (1) Except as provided in paragraph (2)(ii) of this subsection, if a property owner has the exclusive right to use the property and abides by all applicable laws and regulations, a restriction on use regarding land use may not impose or act to impose an unreasonable limitation on the ability of the property owner to develop or offer for rent an accessory dwelling unit. (2) For the purpose of paragraph (1) of this subsection, an unreasonable limitation: (i) Includes a limitation that prohibits, either explicitly or by effect of the restrictions, the development of an accessory dwelling unit; and (ii) Does not include a limitation on the short–term rental of an accessory dwelling unit. (c) This section does not apply to a restriction on use on historic property that is listed in or determined by the Director of the Maryland Historical Trust to be eligible for inclusion in the Maryland Register of Historic Properties.