QUOTE (etherial @ Dec 1 2009, 02:52 PM)

Customizations, Enhancements, Cyberguns, and the like, right?
Please do. I found a page reference in SR3, but they changed how enhancements work for SR4, so I was unsure.
The page you quoted before SR4A, p.313 is the direct quote, but it isn't very specific as to what accessories are.
p. 310 defines Capacity in the sidebar
[ Spoiler ]
QUOTE
Capacity: Some sensor packages and cyberware can be equipped with
a range of subsystems. A Capacity value is listed for these, indicating
the maximum amount of Capacity points worth of accessories it
can hold. The Capacity costs of subsystems/accessories are listed in
brackets. Note that some cyberware items can be installed as standalone
items (taking up Essence only) or as subsystems instead (taking
up Capacity).
Cyberlimb accessories (SR4A, p344) specifically state they can only be installed in cyberlimbs.
The only other relevant quotation I can give is from the FAQ:
[ Spoiler ]
If I install an implant inside a cyberlimb, using up the Capacity of this limb rather than Essence, does the grade of the implant reduce the Capacity cost as it would reduce the Essence cost?
While it makes sense that higher-grade cyberware would take up less space, our answer is no. That's because accessories to an implant must be of the same grade as the implant (the cyberlimb). Since higher-grade cyberlimbs are more compact and efficient in design, however, they have less excess space to fill up. So while the space the accessory takes up shrinks, the space available in the limb also shrinks.
As always, gamemasters can change this if they want. It's not going to be a game breaker to stick a little more gear inside a cyberlimb.
this only reinforces the statement without clarifying.
The seem to be few restrictions on what can be installed save that it must take up capacity and be the same grade.