"description":"A unique key which defines the overwriting semantics for this piece of room state. This value is often a zero-length string. The presence of this key makes this event a State Event. The key MUST NOT start with '_'."
},
"prev_content":{
"title":"EventContent",
"type":"object",
"description":"Optional. The previous ``content`` for this event. If there is no previous content, this key will be missing."