public static bool IsExtraMaterial(string id)
{
return(IsBookIdValid(id) && NonCanonicalIds.Contains(id));
}
/// <summary>
/// True if this is a canonical book id, as opposed to front matter etc.
/// </summary>
public static bool IsCanonical(string id)
{
return(IsBookIdValid(id) && !NonCanonicalIds.Contains(id));
}