Further refine docs

Author: edwardalee

docs/writing-reactors/actions.mdx

@@ -173,20 +173,26 @@ For a **physical** action, the preliminary time is similar, except that _t_ is r
 
 If no `<min_spacing>` has been declared, then the tag of the event is simply the preliminary time
 unless there is already an event scheduled for the same action with the same tag.
-In that case, a microstep is added to the tag.
-If there is again a previously scheduled event with the same tag, then a microstep is added to the tag again.
+In that case, a microstep is added to the tag. If there is again a previously scheduled
+event with the same tag, then a microstep is added to the tag again.
 This process is repeated until there is no previously scheduled event with the same tag.
-This is equvalent to specifying a `<min_spacing>` of 0 with a `"defer"` policy.
 
 If a `<min_spacing>` has been declared, then it gives a minimum logical time
-interval between the tags of two subsequently scheduled events. If the
+interval between the tags of two subsequently scheduled events. The first effect this
+has is that events will have monotically increasing tags. The difference between the
+times of two successive tags is at least `<min_spacing>`. If the
 preliminary time is closer than `<min_spacing>` to the time of the previously
 scheduled event (if there is one), or if the preliminary time is earlier than
 the previously scheduled event, then the time will be modified to enforce
 the minimum spacing. The `<policy>` argument (if supported by the target)
 determines how the minimum spacing constraint is enforced.
-Note that "previously scheduled" here means specifically the tag resulting from
-the most recent call to the schedule function for the same action.
+
+ Note that "previously scheduled" here means specifically the tag resulting from
+ the most recent call to the schedule function for the same action.
+ 
+ A `<min_spacing>` of 0 is not quite the same as no `<min_spacing>` declared.
+ With a `<min_spacing>` of 0, events will still have monotically increasing tags,
+ but the difference between the times of two successive tags can be 0.
 
 <ShowIfs>
 <ShowIf c py>