public void AppendSubtraction(IBaseGroup baseGroup, IExcludedGroup excludedGroup)
{
if (baseGroup == null)
throw new ArgumentNullException(nameof(baseGroup));
if (excludedGroup == null)
throw new ArgumentNullException(nameof(excludedGroup));
AppendCharGroupStart();
baseGroup.AppendBaseGroupTo(this);
AppendDirect('-');
excludedGroup.AppendExcludedGroupTo(this);
AppendCharGroupEnd();
}