{{alias}}( diagonal )
    Returns the enumeration constant associated with a BLAS diagonal type.

    Downstream consumers of this function should *not* rely on specific integer
    values (e.g., `UNIT == 0`). Instead, the function should be used in an
    opaque manner.

    Parameters
    ----------
    diagonal: string
        Diagonal type.

    Returns
    -------
    out: integer|null
        Enumeration constant.

    Examples
    --------
    > var out = {{alias}}( 'unit' )
    <number>

    See Also
    --------