clarify exponential notation and add canonical JSON note

this makes more sense to me

changelogs/room_versions/newsfragments/2297.clarification

@@ -1 +1 @@
-Clarify floaty powerlevels.
+Clarify meaning of floating-point powerlevels.

content/rooms/fragments/v1-floaty-power-levels.md

@@ -1,5 +1,5 @@
 
-##### `m.room.power_levels` Events Accept Values as Floats
+##### `m.room.power_levels` events accept values as floats
 
 When the value is a float, anything after the decimal point is removed,
 making e.g. `5.17`, `5.42`, and `5` functionally identical. 
@@ -31,4 +31,10 @@ For example, this is a valid `m.room.power_levels` event in this room version:
 ```
 
 In this example, both `@bob:localhost` and `@alice:localhost` have the same effective
-power level of `50`, even though the values are visually different.
+power level of `50`, even though the values are technically different.
+
+When a float written in exponential notation is unpacked, the decimal portion is removed
+afterward; for example, `5.114698E4` becomes `51146.98`, which is then truncated to `51146`.
+
+Note that, since this room version does not enforce that events comply with the requirements
+of [Canonical JSON](/appendices#canonical-json), power levels can be formatted as floats.