It would be best if you share details of what version of Jupyter you are using?
And please share details of where you mean by ‘Online says’ because that likely needs updating. Or it is for a particular custom offering of Jupyter and/or offering of an older version (see below).
My guess is you are using outdated details and current Jupyter tech. All current Jupyter tech is built on JupyterLab components, see the bottom of the SO answer here for more on that.
I found at least one thread on StackOverflow with outdated and/or unclear details in the thread and so prompted by this post, I added an updated, unified answer there entitled: