Github user alpinegizmo commented on a diff in the pull request:

    https://github.com/apache/flink/pull/4041#discussion_r119883183
  
    --- Diff: docs/dev/libs/cep.md ---
    @@ -98,48 +128,106 @@ val result: DataStream[Alert] = 
patternStream.select(createAlert(_))
     </div>
     </div>
     
    -Note that we use Java 8 lambdas in our Java code examples to make them 
more succinct.
    -
     ## The Pattern API
     
    -The pattern API allows you to quickly define complex event patterns.
    -
    -Each pattern consists of multiple stages or what we call states.
    -In order to go from one state to the next, the user can specify conditions.
    -These conditions can be the contiguity of events or a filter condition on 
an event.
    -
    -Each pattern has to start with an initial state:
    -
    -<div class="codetabs" markdown="1">
    -<div data-lang="java" markdown="1">
    -{% highlight java %}
    -Pattern<Event, ?> start = Pattern.<Event>begin("start");
    -{% endhighlight %}
    -</div>
    -
    -<div data-lang="scala" markdown="1">
    -{% highlight scala %}
    -val start : Pattern[Event, _] = Pattern.begin("start")
    -{% endhighlight %}
    -</div>
    -</div>
    -
    -Each state must have a unique name to identify the matched events later on.
    -Additionally, we can specify a filter condition for the event to be 
accepted as the start event via the `where` method.
    -These filtering conditions can be either an `IterativeCondition` or a 
`SimpleCondition`. 
    -
    -**Iterative Conditions:** This type of conditions can iterate over the 
previously accepted elements in the pattern and 
    -decide to accept a new element or not, based on some statistic over those 
elements. 
    -
    -Below is the code for an iterative condition that accepts elements whose 
name start with "foo" and for which, the sum 
    -of the prices of the previously accepted elements for a state named 
"middle", plus the price of the current event, do 
    -not exceed the value of 5.0. Iterative condition can be very powerful, 
especially in combination with quantifiers, e.g.
    -`oneToMany` or `zeroToMany`.
    +The pattern API allows you to quickly define complex pattern sequences 
that you want to extract 
    +from your input stream.
    +
    +Each such complex pattern sequence consists of multiple simple patterns, 
i.e. patterns looking for 
    +individual events with the same properties. These simple patterns are 
called **states**. A complex pattern 
    +can be seen as a graph of such states, where transition from one state to 
the next happens based on user-specified
    --- End diff --
    
    ... where transitions from one state to the next occur ...


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