• VLENs may be of any base type, including user-defined types.
• A VLEN must be written and read as a unit. You cannot read part of a VLEN.
• You can have n-dimensional arrays of VLENs. You can read/write subsets of these arrays.
• When reading VLEN you must free the memory that the library had to allocate for it.
• You must use nc_vlen type in C.
• Problematic but possible in fortran 77 and fortran 90.

2009 Unidata NetCDF Workshop for Developers and Data Providers > User Defined Types in NetCDF-4