public abstract static class Section.Builder<T extends Section.Builder<T>>
A builder to build a Section with a SectionLifecycle L. Generated lifecycle classes
will expose a create() method to access a builder and will add methods to the builder to set
all the props defined in the GroupSectionSpec/ DiffSectionSpec. By default the
builder exposes a method that the parent can use to specify an key for its children. The key
should be set every time a parent might have more children with the same SectionLifecycle.