Clarifying the rule on Rejoinders (Opportunity Attacks) and Forced Movement

This issue has caused some confusion. In 4e for example force movement doesnt provoke an 'opportunity attack' so if for example you are blown backwards. In 5e it was redefined to only being provoked by movement that isn't an action or reaction. So for example running away through a spell causing fear would. However the wording was so subtle, stating in spells that such movement was part of a reaction, that it required clarification through twitter.

In Shatterheart the problem is less in that you move under your own force (if not own control) on turn using that turns movement allowance, and you can advance this through a reaction. The consequences of this spelled out with clear examples in a revised section on rejoinders in the adventurers guide. So the definition of movement creating the chance to rejoinder is that it uses your movement allowences, external foces such as gusts of wind, being knocked back etc do not.