  The proton is arguably the most fundamental of Nature's readily detectable
building blocks. It is at the heart of every nucleus and has never been
observed to decay. It is nevertheless a composite object, defined by its
valence-quark content: u+u+d -- i.e., two up (u) quarks and one down (d) quark;
and the manner by which they influence, inter alia, the distribution of charge
and magnetisation within this bound-state. Much of novelty has recently been
learnt about these distributions; and it now appears possible that the proton's
momentum-space charge distribution possesses a zero. Experiments in the coming
decade should answer critical questions posed by this and related advances; and
we explain how such new information may assist in charting the origin and
impact of key emergent phenomena within the strong interaction. Specifically,
we show that the possible existence and location of a zero in the proton's
electric form factor are a measure of nonperturbative features of the
quark-quark interaction in the Standard Model, with particular sensitivity to
the running of the dressed-quark mass.
