Thus, if it is a painting, we may or may not consider the brush strokes or the texture of the canvas as relevant to the content. If that is the case, the text can be rendered by any duplication of the symbols on any sort of medium, while the only reproduction of an image is the image itself. In contrast, within text, we presume coding. Computer languages are built using grammars of textual and numerical symbols which can be analyzed in the same way we solve mathematical formulae. Diagrams and formulae actually operate in a middle ground.
Diagrams look like pictures, but language-like rules govern their interpretation.
One interesting wrinkle is that markup languages like html, the language used on the internet, employ coded instructions governing appearance. Computers add yet more layers between setting and communicative essence like screen size, rendition in greyscale or color. Creating for the computer includes designing for a variety of different output devices and readers all of which will look different to the user, but all of which are expected to present the same information to that user. The computer makes obvious what has always been true. We are more likely to think of computer text as impersonal information.