According to (spanish) Wikipedia, an "easter egg" is

... is a hidden message or capability embedded in movies, television series, ..., software programs, or video games. Among programmers, there seems to be a drive to leave a personal mark, almost an artistic touch on an intellectual product that is by nature standard and functional. These days, Easter eggs aim to entertain, seek new job opportunities, pay tribute to executives, or amuse programmers.

I have no idea who convinced that gullible Wikipedian that software is "standard and functional", but it is true that the urge for software Easter eggs is almost as old as software itself.

Here is a technique I discovered back in kindergarten, when we would draw with lemon juice so that later, magically, the scribble would be revealed by the teacher's lighter (she was probably smoking in the blocks' corner).

So let’s see how to write invisible (digital) text: lemon juice’s Unicode counterpart.

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It is well known that in a git repository we can use a .gitignore file to skip tracking files we do not want to push to the remote repository. If a file matches a .gitignore pattern, it will not appear in git status when you want to add its changes to a commit.

They are typically used to ignore directories where dependencies are installed (e.g. the virtualenv for Python projects, usually found in .venv), temporary files generated by the interpreter or compiler, IDE-specific files, and so on.

They are so common that GitHub offers gitignore templates curated for different programming languages, and tools such as uv init generate a basic .gitignore as part of the boilerplate.

A .gitignore is part of the project (it is committed), and it is important to keep it in the repository so that every collaborator shares the same configuration.

But what if we want to ignore files only locally?

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