Send message to a channel by name or id. File contents are appended to the message text. Message text is limited to 40000 characters - longer text will be automatically sent as a file. For simple text content, the text and file parameters will be used with the file content appended to the text parameter value. Use '--options markdown' to tell Slack to interpret the simple text as Slack markdown. Use '--options markdown=code' to have file content treated as a markdown code block (non-proportional font). Richer content can be defined using Slack blocks (JSON format) provided by one or more content parameters and the file parameter. Block compliant JSON will be included from the first content parameter, then the file parameter, and then the remaining content parameters. Simple text content parameters will be converted to simple text blocks as a convenience. Refer to Slack documentation on block based content. Refer to the Slack markdown reference for the limited support provided for markdown content in Slack.