What do events in a transaction have In common?

[Reference: https://docs.splunk.com/Documentation/Splunk/8.0.3/Knowledge/Abouttransactions, , A transaction is a group of events that share some common characteristics, such as fields, time, or both. A transaction can be created by using the transaction command or by defining an event type with transactiontype=true in props.conf. Events in a transaction have one or more fields in common that relate them to each other. For example, you can create a transaction based on JSESSIONID, which is a unique identifier for each user session in web logs. Events in a transaction do not have to have the same timestamp, sourcetype, or exact same set of fields. They only have to share one or more fields that define the transaction., , ]