HHCODE.BBOX is available since version 2.4.0.
HHCODE.BBOX function returns the bounding box of the given hhcode at the given resolution.
It will first convert the HHCode to the resolution and then compute the bounding box representing the lat/lon of North-Easth and South-West corners of the bbox.
The function accepts 3 different types of HHCode and will return the same type for the resulting HHCode.
Since 2.6.0, the resolution is optional. In that case the length of the input is used to determine the resolution.