public Builder<G, C> constraint(final Constraint<G, C> constraint) {
			_constraint = constraint;
			return this;
		}
The phenotype constraint is used for detecting invalid individuals
and repairing them.

<p><i>Default implementation uses {@code Phenotype::isValid} for
validating the phenotype.</i></p>

@since 5.0

@param constraint phenotype constraint which can override the default
       implementation the {@link Phenotype#isValid()} method and repairs
       invalid phenotypes when needed.
@return {@code this} builder, for command chaining
@throws NullPointerException if one of the {@code constraint} is
        {@code null}.
jenetics/src/main/java/io/jenetics/engine/Engine.java