Motivation - In order to be able to build a forum discussion's post tree, it is necessary to know the ID of the post that is being replied to in "actor replied to post" statements.
Specification - Include the parent ID of the forum post in the "actor replied to post" statements (possibly in estension data)
Finalised state - Statements describing a post reply in a forum discussion contain the ID of the parent post being replied to.
The sections for an enhancement issue are: