Read only Snapshot can mount ?

hi there ...

I have user saying cannot assign drive letter to read only snap shot @ win host . He managed to mask win host but cannot assign drive letter .

This means ,,,,, read only Snapshot cannot be mounted  from host ? ( win and Unix as well )

( Doc says it can be mapped but cannot be write .... I am getting confused ...Page 28 )

https://support.emc.com/docu59699_XtremIO-4.0-and-4.0.1-Storage-Array-User-Guide.pdf?language=en_US