The source iterable.
A new IEnumerable with all sub-iterable elements concatenated into it recursively up.
Returns a new IEnumerable with all sub-iterable elements concatenated into it recursively up to the specified depth.
A new IEnumerable with all sub-iterable elements concatenated into it recursively up.
Returns a new IEnumerable with all sub-iterable elements concatenated into it one level deep.