Our libraries and the tools built upon them are quite different from most others you see in the market: We disallow “invalid” constructs to be modeled any time. And because the tools are backed up by the respective standards meta-model we are very sure about what is allowed and what is not.
Because of that, whatever you export will always be valid BPMN 2.0 (everything else is a bug that needs to be fixed). So technically, you do not need the validation button you mention, even though you may be used to it from other modeling tools 
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Disclaimer: Obviously there is a lot of things you can validate on top of structural BPMN 2.0 compliantness. As I understand you, that is not what you are asking for.