Clarification of @trusted attribute?

[Gary Willoughby]

I know the reason to mark a method as trusted from the docs:

> Trusted functions are guaranteed by the programmer to not 
> exhibit any undefined
> behavior if called by a safe function. Generally, trusted 
> functions should be kept
> small so that they are easier to manually verify.

> Undefined behavior happens when an illegal code construct is 
> executed.
> Undefined behavior can include random, erratic results, 
> crashes, faulting, etc.
> A buffer overflow is an example of undefined behavior.

So would you mark the following with @trusted? The format() 
function is not @safe but what is @trusted really trying to say? 
This method is @safe as far as i'm concerned? The arguments make 
format() @safe? I'm confused.

	/**
	 * Get the current timestamp for the log.
	 *
	 * Returns:
	 *     The current timestamp.
	 */
	private string getTimestamp() const
	{
		auto time = Clock.currTime();
		return format("%d/%02d/%02d %d:%02d:%02d", time.year, 
time.month, time.day, time.hour, time.minute, time.second);
	}