What is the precise meaning of tvm_access_ptr's extent

Hi,
In tvm code, the comment for tvm_access_ptr about extent argument is “The offset and extent are in unit of the DType(including vectorization factor).”. So, can anybody tell me if the extent is from offset or from beginning 0?

My another question is why this extent argument is not exposed in python api(schedule.Buffer.access_ptr)?
In some case like data flow analysis, more exactly memory access info is helpful for pass process.

Thanks.

The extent is from means the access region is in [offset, offset+ extent)