OxyPowerPack included a feature to add custom attributes to any element in Oxygen Builder since OxyPowerPack 1.0. Now, this feature is being added natively to Oxygen for version 3.5, which is currently in beta stage.
The two features can work well together, but it is a good idea, for cleanliness sake, to use just one of them. So, in OxyPowerPack 1.2.5, we added a tool to migrate your HTML attributes to the native Oxygen version.