title: Why VBScript built-in function do have optional parameters or method oveloads, and I can't?
body: <p>I do know VBScript does not have method overloads or optional parameters, but some built in methods like <a href="http://www.w3schools.com/VBscript/func_instr.asp" rel="nofollow"><code>InStr</code></a> (and may others) can be called in different ways (e.g. <code>InStr([start,] string1, string2 [, compare])</code>).</p>
  
  <p>Are they optional parameters or method overloads?</p>
  
  <p>How are they possible?</p>
  
  <p>What is the reason because the language can do this, but the developer not?</p>