Should phobos functions generally be @safe or @trusted?

[Chris Wright via Digitalmars-d]

I wanted to use std.array.insertInPlace in a @safe module. It's not 
marked @safe or @trusted. The string implementation uses pointer 
arithmetic, and the non-string implementation uses memmove.

Should things like this be marked @trusted in general?

Presumably if a function isn't memory-safe, it doesn't just cause memory 
errors arbitrarily; there's likely something the caller has to do to 
ensure the function doesn't crash or cause memory corruption. It seems 
like that should be documented. When it's not documented, I start feeling 
a bit paranoid.

Should it be a bug if a non- at safe, non- at trusted function doesn't document 
what you need to do to call it safely?