Operating with substrings in strings

[Frank Benoit]

> Slicing:
> 
> char[] h = "hello";
> char[] sub = h[1..3] // Slice the string "hello"
> writefln(sub); // Prints "el"
> 
> http://digitalmars.com/d/arrays.html#slicing
> 

I do not know much about UTF8. And I am often not sure if I do string
processing right. Can someone enlighten me?

If I have
char[] str = ... some multibyte utf8 chars;

What does str.length give me. The number of bytes or the number of
characters by looking at every character, which one are multi-bytes?

If I do some slicing (str[3..4]), does the indices slice at these byte
positions and I have the risk of destroying the string or does it look
at the characters to find the start of the third utf8 character?

Or did I miss something completely?