A list of objects to each if which can be associated some kind of quantification, as specified by an extension of a QuantifiedListElement.
Such a list can be used, for example, to set the ingredients of a solution, where each possible ingredient is a compound, and the quantified list element lets you specify the concentration and the units in which it is expressed. Another use is in specifying the densities of channels on a cell where each channel type is associated with a single value for the surface density.
There is a standard user interface to all QuantifiedLists which presents the possible ingredients and allows the quantity of each to be set.
Internally, QuantifiedLists are just normal lists of extensions to QuantifiedListElement. Each such element holds a reference to an item in the target list and any associated data for the present context.