Properties

Events, groups, and sections can all have optional properties. Properties are key-value pairs that are immediately after the first line of an event or group definition, i.e.

2025-04-30: Carpooling to work
  riders: Tom, Jerry
  fee: $4
 
  Some day I'll have my own car

Indentation

While some of examples are indented (like above), indentation in markwhen is optional.

In this example, riders: Tom, Jerry is one key-value pair and fee: $4 is another. They are stored in the event.properties field as an object and may be used by visualizations. Properties must follow on the line(s) after the event or group definition. You can't put properties at the end of an event description or in the middle of it.

Warning

Unlike the header, event properties cannot use multiline list syntax for arrays -- the dash syntax will be interpreted as a list as part of the event description. You'll need to use flow style if you want an array value for an event or group property:

This won't work:

2025-09-04: Meeting
  recipients:
    - Melissa
    - Roger
    - Don

This will work:

2025-09-04: Meeting
  recipients: ["Melissa", "Roger", "Don"]

Timezone

timezone or tz is a special property of an event to set its timezone specifically:

2025-08-03 10am: Meeting
timezone: America/Los_Angeles
 
2025-08-04 11am: Return flight
tz: -5

Event id

Event ids can be used to create relative dates and let subsequent events refer to it:

2025-08-03 10am: Meeting
id: meeting

Prop Order

There is an additonal field on groups and events, propOrder, which is a string[] of keys in the order that they were defined in the document.

For example in the following markwhen document:

2026: Event
fun: yes
travel: ['America', 'Europe', 'Africa']
people: Family

The properties of the (only) event are:

{
  "fun": "yes",
  "travel": ["America", "Europe", "Africa"],
  "people": "Family"
}

while propOrder will be:

["fun", "travel", "people"]

You can use propOrder to maintain order of property definitions, if desired.