Messages can contain any displayable Unicode sequence of characters (all messages must use UTF-8 encoding).
The message must be well-formed JSON. Here's an example:
{
"body" : "This is a line of text.\nAnd this is another one.",
}
Share.to supports a simple form of Markdown for formatting the body of messages.
and can have title field,
{
"title": "Title",
"body" : "This a **bold** message. [Share.to](http://share.to)",
}
Attachments let you add more context to a message, making them more useful and effective.
Messages can have zero or more attachments, defined as an array. Each hash in that array will contain multiple properties: 
The output of that attachement will be something like this:
Messages can be permanent or ephemeral, the Permanent messages will be stored and are available for ever, on the other hand ephemeral messages are only available for the current session of the user who called the command.
For defining a message type you should provide it by messageType field name which accepts either ephemeral or permanent value, the default value of messageType is permanent.
{ "body" : "This is a line of text.",
"messageType" : "ephemeral"
}
