In Tiki17, Annotations supercede inline comments. In Tiki18, Annotations is an experimental optional preference to replace inline comments.
New in Tiki6
When viewing some objects, including wiki pages, you can select a snippet of text and click on the "comment" button which pops up.
Described here: http://dev.tiki.org/wish3167
Since Tiki 11, the "Inline comments" preference (in the Comments control panel) must be enabled.
In-context comments | Contextual comments | Comments inline | Comment inline