Used to add a comment to the left of and encompassing one or more lines, or to indicate that items to the right are subdivisions of the item on the left. Compare }.
Thomas F. Adams, Typographia; Or, The Printer's Instructor: A Brief Sketch: Braces stand before, and keep together, such articles as are of the same import, and are sub-divisions of the preceding articles. They sometimes stand after, and keep together, such articles as make above one line, and have [...] posts after them, which are justified to answer to the middle of the brace. The bracing side of a brace is always turned to that part of an article which makes the most lines.
Bracket на Википедији.Википедији 