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

m.room.power_levels events accept values as floats

When the value is a float

• First, exponential notation is applied: 5.114698E4 becomes 51146.98
• Second, the value is truncated at the decimal point: 51146.98 becomes 51146.

Values outside the range represented by IEE754 binary64 (a "double") cause the powerlevel event to be rejected, as do Infinity, -Infinity and NaN.

For example, this is a valid m.room.power_levels event in this room version:

{
  "content": {
    "ban": 50,
    "events": {
      "m.room.power_levels": 100
    },
    "events_default": 0,
    "state_default": 50,
    "users": {
      "@example:example.org": 100,
      "@alice:localhost": 50,
      "@bob:localhost": 50.57
    },
    "users_default": 0
  },
  "origin_server_ts": 1432735824653,
  "room_id": "!jEsUZKDJdhlrceRyVU:example.org",
  "sender": "@example:example.org",
  "state_key": "",
  "type": "m.room.power_levels"
}

In this example, both @bob:localhost and @alice:localhost have the same effective power level of 50, even though the values are technically different.

Note that, since this room version does not enforce that events comply with the requirements of Canonical JSON, power levels can be formatted as floats.