In addition to the usual text, icons and colors you can add extensive annotations to a cell. Annotations may include any kind of resource: files,image,audio,video,handwritten notes, URLs, etc.
They can be added to column headers as well.
Long tap on any cell or header > Annotation icon (text bubble) menu option, a new screen will be presented allowing you to type your annotation.
All cells that have an annotation are marked with a small black triangle on the top right corner. If that cell has additional resources such as images or audio, the triangle will be slightly bigger.
They will look like this
To remove an annotation, simply delete its text and resources and tap on Done.
With a single tap you'll be able to review the annotations in any cell/header. If you tap on the small bubble, the original annotation window will appear
Review all annotations of a single studentDouble tap on a student > annotations