[CF-metadata] mass_fraction

[Heinke Hoeck]

mass_fraction description:

Mass fraction is used in the construction mass_fraction_of_X_in_Y,
where X is a material constituent of Y. It means the ratio of the
mass of Y to the mass of X (including Y).

Please check carefully the occurrence X and Y in the last sentence.
Shouldn't it read:
'It means the ratio of the
mass of X to the mass of Y (including X).'

Best regards
Heinke