Name of the font used to print line numbers on the left margin.
If this property is unspecified, the text body font is used.
Accepted values are strings representing a font description Pango can understand. (e.g. "Monospace 10"). See [ [email protected]_string] for a description of the format of the string representation.
The value of this property cannot be changed anymore after the first call to the [[email protected]] function.