There are a couple of options. A quick method would be to put text onto the page, but make the text white. When highlighted, the text will be visible, but otherwise not. The downside is that students can easily see the comments by doing the same way. It will also leave visible gaps in the text.
Another way is the HTML editor. Traditional HTML comments will work, but every time you open the editing pane to look at them, you will get notice of "auto-saved content" asking if you want to load it. If you say no...the comment disappears.
A way around this is to set a division, but with a tag to display nothing. This will require you to visit the HTML editor every time you want to review comments, so only you (or another teacher using the course) can see the comments. To do this, use the following in the HTML editor (remember that the Pretty Editor defaults to the bottom of the page, so putting the code at the end of everything will reduce your need to search for it):
<div style="display: none;">Comments go here</div>
Then put your comments in the spot marked. This works well if you just want to have some notes all in one spot.
If you want to put notes throughout your page, then we can look at an alternative way to implement divisions. A slight variation to the HTML looks like this:
<div data-comment-abc123="This is a general comment that does not affect the look of the page">Put your normal content here.</div>
For this option, the part that says data-comment-abc123 is a bit modifiable, a bit not. The part in red needs to be kept intact, but you can modify the part in green. Put whatever notes you want inside the quotation marks (part in blue). The part in orange is where you can put all of the content you want students to see. If you remove any of the part in red, it will strip out the comment and leave just <div>, so just be careful about that. You could feasibly set up a system for yourself. So the part that says -abc123 could be -teaching_note, -revise, -citation, etc. as reminders to yourself about the notes.
Hopefully, one of these might provide an option to consider for putting the comments on the page.
