/// <summary>
/// Composes this with the given builder and updates <seealso cref="isComplete()"/> with the provided builder. </summary>
/// <param name="contentBuilder"> that will be combined with this builder </param>
/// <returns> The combined builder </returns>
/// <exception cref="IllegalStateException"> if the current builder is already complete </exception>
public virtual ContentBuilder <CONTENT> Combine(ContentBuilder <CONTENT> contentBuilder)
{
if (_isComplete)
{
throw new System.InvalidOperationException("This content builder has already completed and cannot be combined.");
}
_contentFunction = _contentFunction.compose(contentBuilder._contentFunction);
_isComplete = contentBuilder._isComplete;
return(this);
}