Mass fraction is used in the construction mass_fraction_of_X_in_Y, whereX is a material constituent of Y. It means the ratio of the mass of X to the mass of Y (including X). A chemical species denoted by X may be described by a single term such as 'nitrogen' or a phrase such as 'nox_expressed_as_nitrogen'. "Clox" describes a familyof chemical species consisting of inorganic chlorine compounds with the exception of hydrogen chloride (HCl) and chlorine nitrate (ClONO2). "Clox" is the term used in standard names for all species belonging to the family that are represented within a given model. The list of individual species that are included in a quantity with a group chemical standard name can vary between models. Where possible, the data variable should be accompanied by a complete description of the species represented, for example, by using a comment attribute. "Inorganic chlorine", sometimes referred to as Cly, describes a family of chemical species which result from the degradation of source gases containing chlorine (CFCs, HCFCs, VSLS) and natural inorganic chlorine sources such as seasalt and other aerosols. Standard names that use the term "inorganic_chlorine" are used for quantitiesthat contain all inorganic chlorine species including HCl and ClONO2. The phrase 'expressed_as' is used in the construction A_expressed_as_B, where B is a chemical constituent of A.It means that the quantity indicated by the standard name is calculated solely with respect to the B contained in A, neglecting all other chemical constituents of A.