private void RejectDuplicates(string name)
{
var existing =
new ListOf <string>(
new Yaapii.Atoms.Enumerable.Mapped <XElement, string>(
elem => elem.Name.LocalName.ToLower(),
this.node[0].Elements()
)
);
if (
existing.Contains(name.ToLower())
)
{
throw new InvalidOperationException($"Cannot add '{name}' because it already exists.");
}
}
