I learned some html long ago. It's changed a lot since then. CSS. I never got into. XML might be interesting IDK. That's all browser stuff though.I know html and css
I know a little html css and python. Some markdown too. Learned bits of SQL and bits of R as well.
What would you use R for ? I don't think Ruby is that popular. The guy that wrote it wrote objective C then left it. SQL isn't that for databases? C/C++ would be for writing the databases. I like POSIX systems anyway. UNIX, linux, minix.
Many. including php & mysql.
JS object notation.And what do you mean JSON related stuff ? Isn’t that just a notation . It is used by miscroservice developers a lot of they are playing with postman and testing it .. and front end developers when they consume said APIs .