This callback is fired when a user clicks a tab on the property page, and when the property page is opened.
The OnTab callback is not fired if the property page is displayed as a list.
To access the property page from the callback code, use the PPG object.
Custom Properties implemented in a scripting language.
| 
function <property_name>_<tab_label>_OnTab()
{ 
        ... 
}
 | 
| 
def <property_name>_<tab_label>_OnTab():
        ...
 | 
| 
Function <property_name>_<tab_label>_OnTab()
        ...
End Function
 | 
| 
sub <property_name>_<tab_label>_OnTab 
{ 
        ... 
}
 | 
<property_name> is the name specified in the call to PluginRegistrar.RegisterProperty, with any spaces converted to underscores. For example, if you register a property with the name "My Property", the callback function names start with "My_Property".
<tab_label> is the label specified in the call to PPGLayout.AddTab, with any spaces converted to underscores.