What is "sidenote"

Usage examples of "sidenote".

Some of these sidenotes were at the beginning of a paragraph, some were placed elsewhere alongside a paragraph, in relation to what the sidenote referred to inside the paragraph.

As a sidenote, I learned that Alexius befriended the sons of Romanus IV Diogenes.

In this e-text, sidenotes that appeared at the beginning of a paragraph in the original book are placed to precede their reference paragraph.

All other sidenotes have been enclosed in square brackets and placed into the paragraph near where they were in the original book.

If there were sidenotes, they would be printed in the wide margin, outside the line.