Oxygen allows you to add custom HTML attributes to elements. You can find this option in the Advanced Tab of the Properties Pane, in the Attributes control section.
To add an attribute to an element, click the Add Attribute button. You can add multiple attributes to each element.
You can use the Dynamic Data buttons in the name and value fields to insert dynamic data.
To remove an attribute, click the x icon to the right of the attribute you'd like to remove.