What does it mean: buffer[0 .. kSize] = input[index .. (index + Size)];

[t0mek]

Hello,
I found some code in D and I am wondering what does it mean:
buffer[0 .. Size] = input[index .. (index + Size)];

I understand it can be written like this:
for (i=0; i<Size; i++) buffer[i]=input[i+index];
But...
1) does it allocate space for buffer?
2) if buffer has already some data- will be zeroed?
3) if there is no enough date (less then Size) in input will there be an 
exception or will be copied what already is in the array?

Regards,
t0mek