Could you elaborate on your design and explain what the acronym's mean?
Any: A pointer to anything.
Refco: Reference counter.
Fl: Flags.
T: Type.
PVX: Pointer value (a pointer to a string).
CUR: Length of above string.
LEN: Size of allocated area for string.
IVX: Integer value.
For an SvIV, the PVX, CUR and LEN values are unused.