There are some times when you want to leave a note to the reader of remarkup source, but not have it on the page. For example, "/* sort this list by last name */" or "/* make sure that changes to this pages are approved by that guy */" or whatever other information might be sensible to tell editors.
It would be nice to support a comment syntax that isn't actually rendered.
What problem specifically are you having using Phabricator? Is this Phriction, Maniphest, something else? What are you trying to do? How often do you need to leave notes, who are the left for, should they be restricted in viewing.
You're continuing to ask for features and without describing the problem. I understand it's likely the norm for most open source projects to work like that, but we're trying to be much more tactical with our feature-set given there are only three developers. Please take the time and just tell us what you're having problems with, there is likely already another solution sitting in Maniphest.
https://secure.phabricator.com/book/phabcontrib/article/feature_requests/#describe-problems
T1894 discusses something similar, but only for Phriction. It may or may not be what you're looking for.
In this case I tried to describe the problem as well, but let me try differently.
This is for phriction, the wiki. They don't have to be restricted for viewing (in the sense that they should be part of the normal editing markup of the page). It is particularly useful for tables with certain sort orders. In addition, certain pages may have lists of things that need to affect external systems, so it is helpful to add a reminder to the editor of such a page.
I am talking about leaving non-rendered notes for future editors of a particular wiki page.
The syntax might also be helpful to hide not-yet-completed text (though this isn't the exact use case I have in mind)
(T1894 is a different term comment, thats for discussing the page, rather than the <!-- --> style comments I'm talking about)
Best way to think about it for me is, plead a real use case, something that is bothering you on a day to day basis. Real problems from real use get our attention best. We try to separate out the 'wouldn't it be cool if...' tasks from the 'this would save me 5 real minutes a day' tasks. We also, if you haven't noticed, like to over-engineer things when possible.
In CMS systems it's common to have documents that have mixed permissions, so some content is "public" and other content is "content creators only". I personally prefer to beef up Phriction if possible, but maybe @epriestley has other thoughts.
So, this isn't really related to being a CMS, though having that ability might be nice (though much more complex). This task comes from a real use case. I am looking at migrating an existing wiki, and we have comments like "this list must be kept in sorted order" or "if you change this list, also modify that XML file". While I could translate these to small font italics or something, having a real comment syntax would be nice.