If a plug is not enabled, this will be populated with indexes into the plug item
definition's plug.enabledRules property, so that you can show the reasons why it
is not enabled. [...]
If the plug cannot be inserted for some reason, this will have the indexes into
the plug item definition's plug.insertionRules property, so you can show the
reasons why it can't be inserted. [...]
Sometimes, Plugs may have objectives: these are often used for flavor and
display purposes, but they can be used for any arbitrary purpose (both
fortunately and unfortunately). Recently (with Season 2) they were expanded in
use to be used as the "gating" for whether the plug can be inserted at all. For
instance, a Plug might be tracking the number of PVP kills you have made. It
will use the parent item's data about that tracking status to determine what to
show, and will generally show it using the DestinyObjectiveDefinition's
progressDescription property. Refer to the plug's itemHash and objective
property for more information if you would like to display even more data.
