I want to create a macro `\verticalStep` which will produce a vertical skip of fixed length, and take two optional arguments, `negative` and `small`.

So for you could use

* `\verticalStep` for a standard vertical skip
* `\VerticalStep[negative]` for reducing vertical skip by standard length
* `\verticalStep[small]` for a small fixed vertical skip
* `\VerticalStep[negative, small]` for reducing vertical skip by small standard length

I have been looking into `xkeyval` and `pgfkeys` and could not for the life of me find a simple or straightforward example of how I may go about parsing the argument and checking for the options. I managed to find [this](https://tex.stackexchange.com/questions/444146/define-command-macro-with-boolean-flag), but the only answer uses expl3 and I wonder if there is a more elegant solution that does not require switching syntax