3-d references

Continuing the same question...

Given the same reference below (=SUM(['Sheet1'.B4:'Sheet2'.C5])), does the specification explicitly define this to be the sum of B4:C5 on sheet1, sheet2 and any sheets in between?  For references, this seems to be equivalent to an Excel 3d reference of the type SUM(['Sheet1':'Sheet2'.B4:C5]

Thanks,
Eric Patterson
Program Manager
Microsoft Excel