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'. "Brox" describes a family of chemical species consisting of inorganic bromine compounds with the exception of hydrogen bromide (HBr) and bromine nitrate (BrONO2). "Brox" 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 accompaniedby a complete description of the species represented, for example, by using a comment attribute. "Inorganic bromine", sometimes referred to as Bry, describes a family of chemical species which result from the degradation of source gases containing bromine (halons, methyl bromide, VSLS) and natural inorganic bromine sources such as volcanoes, seasalt and other aerosols. Standard names that use the term "inorganic_bromine" are usedfor quantities that contain all inorganic bromine 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.