Files
Image preview
You can drop any image available in the folder of your notebook and type in a new cell its filename
randompic.png
Reading and writing files
In principle you can print the content of any file located in the notebook's folder by typing its name without line breaks
filename.txt
For writing this is the same, but the actual content goes from the next line
filename.txt
Hello World
Or, if you are writing a package, it will come handy
cell 1
IR.wl
BeginPackage["JerryI`Mirage`IR`"]
(* utils *)
MapHeld[f_, list_] := Table[Extract[Unevaluated[list], i, f], {i, 1, Length[Unevaluated[list]]}]
SetAttributes[MapHeld, HoldAll]
ClearAll[Lexer]
SetAttributes[Lexer, HoldAll]
...
And then, it can be imported easily
cell 2
Get["IR.wl"];
info
Frontend detects the file extension and tries to find a proper syntax highlighting scheme.