FeatureGroup is a specialization of the FeatureTreeNode, enabling grouping of several Features.<br/><br/>Semantics:<br/>FeatureGroup is a grouping entity for sibling Features to reflect variability for a set of Features.<br/><br/><br/>Extension:<br/>Class<br/>
The cardinality of the FeatureGroup, specifies how the grouped features, in featureGroup, can be combined. For example, a FeatureGroup owning the two Features A and B, and with a cardinality of [1], means that A and B are alternatives, but only one of them can be chosen. Mandatory features among the child features count as 1 and for cloned features all instances created in the configuration count.<br/>
Name: childFeature
FeatureGroups may only have Features as their children and must always have at least two children.
It is perfectly legal to have child features in a feature group that are mandatory or cloned. However, except for special use cases, this is discouraged and therefore all child features of a FeatureGroup should usually be optional, i.e. have cardinality [0..1].
