  We consider a voting model, where a number of candidates need to be selected
subject to certain feasibility constraints. The model generalises committee
elections (where there is a single constraint on the number of candidates that
need to be selected), various elections with diversity constraints, the model
of public decisions (where decisions needs to be taken on a number of
independent issues), and the model of collective scheduling. A critical
property of voting is that it should be fair -- not only to individuals but
also to groups of voters with similar opinions on the subject of the vote; in
other words, the outcome of an election should proportionally reflect the
voters' preferences. We formulate axioms of proportionality in this general
model. Our axioms do not require predefining groups of voters; to the contrary,
we ensure that the opinion of every subset of voters whose preferences are
cohesive-enough are taken into account to the extent that is proportional to
the size of the subset. Our axioms generalise the strongest known satisfiable
axioms for the more specific models. We explain how to adapt two prominent
committee election rules, Proportional Approval Voting (PAV) and Phragm\'{e}n
Sequential Rule, as well as the concept of stable-priceability to our general
model. The two rules satisfy our proportionality axioms if and only if the
feasibility constraints are matroids.
