ent under normal conditions, but if the function manually assigns a value to the missing parameter prior to the IsMissing call then the behaviour may not match that of VB, since the <tt class="literal"><span class="pre">vbfunctions.IsMissing</span></tt> function has no way to detect that the parameter was not supplied.</p>
<p>VB:</p>
<pre class="literal-block">
Dim moduleGlobal1, moduleGlobal2

Function MyFunc(X, Optional Y, Optional Z=20)
    Dim subLocal
    If IsMissing(Y) Then Y = 12
    subLoca