Information about milestones, presented in a character state-agnostic manner. Combine this data with DestinyMilestoneDefinition to get a full picture of the milestone, which is basically a checklist of things to do in the game. Think of this as GetPublicAdvisors 3.0, for those who used the Destiny 1 API.
Type: object
Object Properties
Mapped to Definition
The hash identifier for the milestone. Use it to look up the DestinyMilestoneDefinition for static data about the Milestone.
Type: uint32
Mapped to Manifest Database Definition: Destiny.Definitions.Milestones.DestinyMilestoneDefinition
A milestone not need have even a single quest, but if there are active quests they will be returned here.
Type: array
Sometimes milestones - or activities active in milestones - will have relevant vendors. These are the vendors that are currently relevant.

Deprecated, already, for the sake of the new "vendors" property that has more data. What was I thinking.
Type: array
Array Contents: uint32
This is why we can't have nice things. This is the ordered list of vendors to be shown that relate to this milestone, potentially along with other interesting data.
Type: array
If known, this is the date when the Milestone started/became active.
Type: date-time
If known, this is the date when the Milestone will expire/recycle/end.
Type: date-time
Used for ordering milestones in a display to match how we order them in BNet. May pull from static data, or possibly in the future from dynamic information.
Type: int32