Judging from the letter from the editor, my previous understanding was wrong, and I am deeply sorry for the inconvenience caused by biomedweb. I have a new understanding, but I'm not sure if it's correct. I put it forward here for your reference. According to the editor's explanation, the table of contents should be a small gray map, but it is not the table of papers, but the map needed for editing and sorting out the whole periodical table of contents. The chart should reflect the main points of the paper, which can be structure chart, curve chart, drawing, gel electrophoresis chart or flow chart. , which can be in any format of PDF, TIFF, JPEG or GIF, not higher than 3cm and not wider than 6cm. In fact, some domestic periodicals are also like this. For example, the Journal of Inorganic Chemistry will give a picture under the title of each article in the English catalogue of the journal. In the words of the journal submission instructions, it is "to edit the English catalogue with pictures or schematic descriptions (such as pictures or reaction diagrams) and a short text description that can reflect the main points of the full text and guide readers to read".