What exactly does the colon ":" (statement delimiter) do in VBA?

":" meant as a "newline" fails to explain this behavior:  

This 3-lines code compiles successfully:

```
If 1 = 2 Then
    MsgBox "impossible"
Else: MsgBox "OK": End If

```

This 2-lines version fails with "Compile error: Else without If":

```
If 1 = 2 Then: MsgBox "impossible"
Else: MsgBox "OK": End If

```

This 1-line version fails with "Compile error: End If without block If":

```
If 1 = 2 Then: MsgBox "impossible": Else: MsgBox "OK": End If

```

So, how the meaning of ":" be exactly described, compatibly with these behavior?