This ticket is about adding powerful Custom events feature to Piwik.

Use cases:
- Mobile events analytics
- API analytics #4178
- JS error tracking #4977
- Offline tracking, Retail analytics
- Tracking actions by users or customers
– Getting useful aggregate reports on these actions, overall, averages, relative values.
- Web form analytics #562

An EVENT is defined by:

```
- Category
- Action
- Name
- Value
```

Event Metrics are in Events Overview report:
– Total number of events
– Unique events
– Visits with events
– Events/visit
– Event value
– Average event value AVG

MAIN REPORTS:

```
- Top Event Category (total events, unique events, event value, avg+min+max value)
- Top Event Action (total events, unique events, event value, avg+min+max value)
- Top Event Name (total events, unique events, event value, avg+min+max value)
```

COMPOSED REPORTS

```
- Top Category > Actions X
- Top Category > Names X
- Top Actions > Categories X
- Top Actions > Names X
- Top Names > Actions X
- Top Names > Categories X
```

UI
– Overview at the top (graph + Sparklines)
– Below show the left menu UI selector

Not MVP (move to other ticket)
– On hover on any row: Show % of total events
– Add min value metric, max value metric in tooltip
– List event scope Custom Variables Names > Custom variables values > Event Names > Event Actions
– List event scope Custom Variables Value > Event Category > Event Names > Event Actions

Done before 2.2.0:
- Tracking API (Javascript and HTTP)
– trackEvent( category, action, [[value](name],) )
- Events Segments
- Display events in Live/ [Visitor log](http://piwik.org/docs/real-time/) / [Visitor profile](http://piwik.org/docs/user-profile/)

Done in 2.2.0:
- Documentation
– add trackEvent to [Javascript tracker](http://developer.piwik.org/api-reference/tracking-javascript)
– Add new user manual for [Custom Events Analytics](http://piwik.org/docs/event-tracking/)

References:
- See Google Analytics API: [image](http://blogoscoped.com/files/google-analytics-event-tracking-large.png), [guide](http://code.google.com/apis/analytics/docs/eventTrackerGuide.html), [extending tracking](http://code.google.com/apis/analytics/docs/eventTrackerWrappers.html)
- trackEvent(category, action, label, value)