BoxConstraints additionalConstraints

Additional constraints to apply to child during layout

Source 

BoxConstraints get additionalConstraints => _additionalConstraints;
void additionalConstraints=(BoxConstraints newConstraints)

Source 

set additionalConstraints (BoxConstraints newConstraints) {
  assert(newConstraints != null);
  assert(newConstraints.debugAssertIsValid());
  if (_additionalConstraints == newConstraints)
    return;
  _additionalConstraints = newConstraints;
  markNeedsLayout();
}