Dress rehearsal for your commits
The mobile app can now ask the server to draw a draft exactly as it will look once posted. Emoji are swapped, code is highlighted, mentions are marked. Nothing is saved, and your posting budget is untouched.
You're typing a reply in the app and tap preview. You type the shortcode :rocket:. It becomes a rocket. Your fenced PHP block comes back syntax-colored, and @nunomaduro is flagged as a mention, with its offset and length so the app can link it. It is the commit card you already know, drawn from the same pieces the app uses for posted commits, except nothing has been posted.
Credit goes to simonhamp, who gave the app the server's version of the web composer's preview. Runs of blank lines collapse to one, shortcodes become emoji, code is split into prose, inline code and highlighted blocks, and code keeps its blank lines while mentions inside it are ignored. A draft can run 4,000 characters, each link counting as 23, or up to 40,000 raw characters when links pad it out. Anything over 280 characters or 8 lines also comes back folded to a list-sized excerpt.
One catch. It previews words only. The request carries a body and nothing else, so no link card is fetched, and a poll, photos or a quoted commit never show up in the answer. You see the text card, not the whole commit as it will post.