  Extremely compliant elastic materials, such as thin membranes or soft gels,
can be deformed when wetted by a liquid drop. It is commonly assumed that the
solid capillarity in "soft wetting" can be treated in the same manner as liquid
surface tension. However, the physical chemistry of a solid interface is itself
affected by any distortion with respect to the elastic reference state. This
gives rise to phenomena that have no counterpart in liquids: the mechanical
surface stress is different from the excess free energy in surface. Here we
point out some striking consequences of this "Shuttleworth effect" in the
context of wetting on deformable substrates, such as the appearance of elastic
singularities and unconventional capillary forces. We provide a synthesis
between different viewpoints on soft wetting (microscopic and macroscopic,
mechanics and thermodynamics), and point out key open issues in the field.
