Hi!
The verbose form of incrementing is supported. For instance, your “plus” button could say:
OnClick
Set text of (widget) "counter" to (value) [[Target.text + 1]]
…no global variables required. Similarly, if you wanted to increment the text in a widget by clicking the widget itself, you could say:
OnClick
Set text of (widget) This to (value) [[This.text + 1]]
If you need to access properties of widget that is neither the target of the command or the receiver of the event, you’d use a local variable where Target or This above sits.
The global variable “varName” can be incremented with:
Set varName to (value) [[varName + 1]]
You are correct that [[varName++]] is not supported.