At the side of a writing or between paragraphs of text, you can place an area to provide additional information, a summary etc., which is called a "sidebar" in the publishing "scene", but in this service it has already become known as a sidebar. It is possible that this may be confused with a slightly later feature, which has been provisionally named "sideshow" and which is basically a sidebar at the side of the front page of a work, where basically anything can be placed (statistics, advertisements etc.). Here are a few available sidebar border style adjustments to make it stand out from the rest of the text.
You can use images as content in these writings, but not pictureshows, nor anything embeddable. Due to memory load, it might be advisable to initially keep them in the same writing collection as the writings they are part of. In the fine-tuning writings view, hovering a pointer over a writing that uses one of these will cause the included writing to indicate its inclusion visually if they are in the same writing collection. All kinds of writings can be freely moved within the project boundaries from one writing collection to another without worrying about breaking integrity.