Use the Generate Composite option when creating a ConnectFX if you want to convert any existing Timeline FX to a ConnectFX pipeline. When you enter ConnectFX, you'll see that your pre-existing Timeline FX are now displayed as ConnectFX nodes, allowing you to edit these effects directly in the ConnectFX view, or add or delete as many other effects as needed.
In the case of entering ConnectFX with multiple video elements, you can also see that upon exiting ConnectFX, only one element exists, comprising the composite of the previous elements. To restore your previous vertical edit on the timeline, you can click Remove CFX and Recover Stack. The previous configuration of the video elements is restored, but any pre-existing Timeline FX are lost.
You can create an edit on the timeline in a gap above multiple clips, without losing any of the effects already on those clips. After creating an adjustment segment, you can add new clips or edit existing clips on the timeline under the adjustment segment gap, and the ConnectFX is maintained above. You can perform edits on an adjustment segment as it is treated like any other timeline segment, such as trimming or even adding other Timeline FX.
The adjustment segment uses the top media of the tracks below the timeline gap as the input. Inside ConnectFX, that input is called the Back Clip. For example, if you have three tracks composited together, and you add an adjustment segment on top of them, the image available through the Back Clip is only the output of the third track.
The Back Clip node is available in the ConnectFX I/O bin. The Back Clip node does not contain any media; instead, it offers a link to the Timeline, giving access to the topmost media located below the CFX segment you are currently working on. Since the Back Clip is only a link to media, you cannot access common clip settings within ConnectFX. The only settings that are available if you double-click the Back Clip node are to set what media is available for the head and tail of the adjustment segment.