Assault: Line of Sight

[atatnet]

To be able to assault, a unit must be able to 'see' the target of the assault from the starting position. (pg 28, first line)

What are the rules for line of sight for Assault purposes? Is a unit able to see through another friendly unit in the open?

Examples:
1. Can AAAA see through friendly line infantry XXXX to assault enemy TTTT?:

AAAA
XXXX

TTTT

2. Can AAAA see through friendly line infantry units XXXX and YYYY to assault enemy TTTT? The gap in between XXXX and YYYY is one base width. Ignore the ooo, its just there for spacing purposes:

oooAAAA
XXXX YYYY

oooTTTT

[terrys]

Units do not block line of sight.

[atatnet]

OK. Thanks.

BTW, this is not explicitly stated in the rules. I got initially thought it had something to do with the LOS for Firing.