The support for Constraints seems very counter-intuitive.
a) A Constraint must be dropped as a top-level diagram element;
a Properties entry does not seem to be present.
b) The Constraint can then be given a Context from the Properties
drop-down; an edge does not seem to be possible.
c) The Properties offers a large 'Constrained Elements' entry field,
but only a small Specification field.
d) The Specification field allows only selection of literals already
defined; no ability to create a new OCL expression.
e) Giving an operation constraint a BodyCondition role is not possible
using e.g. a <<body>> sterotype.
f) The Specification is not displayed within the {} of the Constraint.
It seems that Papyrus provides some creation help through the Constraint
node but full entry requires detailed understanding of UML and use of
the UML2 model level editing.