The Highlightr plugin enables this (at the cost of littering your text with HTML).
- Annotations
I use comments placed after highlights.
==I highlighted this text.==%%And commented on it.%%
(Actually I use <!--HTML comments--> for better readability and compatibility.)
- Managing both highlights and annotations
I use an embedded search: List all highlights in document(s) — without community plugins. It’s not completely smooth, but it works well enough for me. If someone would package up the same basic idea in a plugin, that would smooth out the rough edges (maybe someday I’ll learn how).
KEEP ON ROCKING!