Returning reference: why this works?

[Denis Feklushkin via Digitalmars-d-learn]

import std.stdio;

struct S { int x; }
ref S func1(ref S i) // i is reference
{
    return i;
}

ref S func2(S i) // i is not reference
{
  return func1(i); // Works! Possibility to return reference to 
local object i?
  //return i; // Error: returning i escapes a reference to 
parameter i
}

void main() {
  auto ret = func2(S(2));

  writeln(ret); // "S(2)"
}