Posting formats and different styles of displaying them

It is possible to add a field to posting's body that describes its format. For example, a Facebook-style "brick" with large text and colored background will be described as:

{
    body: "<p>Hello, world!</p>",
    format: "brick",
    brick: {
        color: "#abcdef"
    }
}

The actual display of the posting depends on the client. Some formats may be not supported by some clients or user may choose not to display them or display differently. For example, those who do not like "bricks" may choose to display them as regular posts.

Start by reviewing the proposed posting payload and the distinction between the posting format and client-side display. The issue names no files, tests, or entry points, so the first step is to locate the posting schema and relevant client handling. Done would require an agreed format model and defined behavior for supported and unsupported formats.