core/homeassistant/components/matrix/services.yaml

send_message:
  name: Send message
  description: Send message to target room(s)
  fields:
    message:
      name: Message
      description: The message to be sent.
      required: true
      example: This is a message I am sending to matrix
      selector:
        text:
    target:
      name: Target
      description: A list of room(s) to send the message to.
      required: true
      example: "#hasstest:matrix.org"
      selector:
        text:
    data:
      name: Data
      description: Extended information of notification. Supports list of images. Supports message format. Optional.
      example: "{'images': ['/tmp/test.jpg'], 'format': 'text'}"
      selector:
        object: