Comments

Ctrl + Shift + M annotates a word, a line or the line of an image, without changing its text. Without a selection, it comments the line.

In the file

The comment is kept in the note itself, as CriticMarkup:

{==the text==}{>>the comment<<}

The file stays plain Markdown. In Bref, the text is highlighted and the comment follows it, faded.

A panel to the right of the note lists its comments.

Click a comment to go to it.
Click its check mark (it shows under the pointer) to resolve it: the markup goes, the text stays.
The comment of the passage under the caret is on a tint, and the panel scrolls to it.
The speech bubble at the bottom right of the note, next to the copy button, closes and opens the panel. So does the panel's cross.
A badge on the bubble counts the comments (9+ beyond nine).
comments in the palette lists them, to jump to one from the keyboard.

On a comment, Ctrl + Shift + M resolves it. On a line of its own (see below), the line goes.

A cell: the comment is on the text of the cell. A selection over several cells gets one comment per cell, never across a |. A | typed in the comment is written \|.
A row, a column or the whole table, taken by its grip: the comment goes on a line of its own under the table, named by its content. A row is named by its first cell, a column by its header: {>>Column "Age": in years<<}.

Because the comment is named by content, a sort leaves it where it belongs:

Renaming that first cell or header renames the comment.
Deleting the row, the column or the table deletes it.
Moving, inserting, duplicating, sorting or swapping rows and columns keeps it with what it is about. One Ctrl + Z brings both back.

How it shows:

A commented cell is tinted, with a mark in its corner.
A commented row, column or table is outlined, with a dot on its grip. It is stronger while the cursor is in the comment.
The panel says where each comment is: Cell C2, Row Léa, Column Age, Table.

A comment on an empty cell is refused: there is nothing to highlight.