It’s a text editor. It can edit text just fine. If you need to do esoteric stuff like opening/saving you might as well install Visual Studio or something.

You can open and save. Just use the browser's save function, to save a local HTML file. (At least on my computer, this saves the text you put in, at least if you select the "complete" option when saving.) You can then recall that file just as easily.

Of course, it will only save as HTML and recall the same HTML file you saved in this way, and doesn't support plain text files. But, nevertheless, you can open and save.