...| --> app events such as IMPRESSION, FEEDBACK, etc may happen
| --> IMPRESSION - For the pages that the user visits
| --> INTERACT --> one of the content is clicked
| --> START(type: "player") --> events generated by specific content
...| --> in-content events such as ASSESS, INTERACT, IMPRESSION, LEVEL_SET etc.
| --> END(type: "player")
| --> IMPRESSION - Returned back to mobile app for content player
...| --> app events such as IMPRESSION, INTERACT, etc. may happen
| --> INTERACT --> one of the content is clicked
| --> START(type: "player") --> events generated by specific content
...| --> in-content events such as ASSESS, INTERACT, IMPRESSION, LEVEL_SET etc.
| --> END(type: "player")
| --> IMPRESSION - Returned back to mobile app for content player
...| --> app events such as IMPRESSION, INTERACT, etc. may happen
...| --> app events such as APP_UPDATE, FEEDBACK, etc may happen