Directly changing array values.
string(10) "original.1"
string(10) "original.2"
string(10) "original.3"
array(3) {
  [0]=>
  string(9) "changed.0"
  [1]=>
  string(9) "changed.1"
  [2]=>
  string(9) "changed.2"
}

Modifying the foreach $value.
array(3) {
  [0]=>
  string(10) "original.1"
  [1]=>
  string(10) "original.2"
  [2]=>
  string(10) "original.3"
}

Modifying the foreach &$value.
array(3) {
  [0]=>
  string(9) "changed.0"
  [1]=>
  string(9) "changed.1"
  [2]=>
  &string(9) "changed.2"
}

Pushing elements onto an unreferenced array.
array(6) {
  [0]=>
  string(10) "original.1"
  [1]=>
  string(10) "original.2"
  [2]=>
  string(10) "original.3"
  [3]=>
  string(5) "new.0"
  [4]=>
  string(5) "new.1"
  [5]=>
  string(5) "new.2"
}

Pushing elements onto an unreferenced array, using &$value.
Loop detected
array(15) {
  [0]=>
  string(10) "original.1"
  [1]=>
  string(10) "original.2"
  [2]=>
  string(10) "original.3"
  [3]=>
  string(5) "new.0"
  [4]=>
  string(5) "new.1"
  [5]=>
  string(5) "new.2"
  [6]=>
  string(5) "new.3"
  [7]=>
  string(5) "new.4"
  [8]=>
  string(5) "new.5"
  [9]=>
  string(5) "new.6"
  [10]=>
  string(5) "new.7"
  [11]=>
  &string(5) "new.8"
  [12]=>
  string(5) "new.9"
  [13]=>
  string(6) "new.10"
  [14]=>
  string(6) "new.11"
}

Popping elements off an unreferenced array.
string(10) "original.1"
string(10) "original.2"
string(10) "original.3"
array(0) {
}

Popping elements off an unreferenced array, using &$value.
string(10) "original.1"
string(10) "original.2"
array(1) {
  [0]=>
  string(10) "original.1"
}