[Dev-luatex] tex.sp error handling

Hi, if I understand things right, this code will not reach the second line. local ret = tex.sp("1cow") print(type(ret)) Instead, TeX stops (at least in my source code, I could have done something wrong) with "Illegal unit of measure (pt inserted)". Would it be possible to have some nicer error handling? For example to return [ nil, "Illegal unit of measure (pt inserted)"] ? Patrick