If a newline character has this property, it is a “hard” newline.
The fill commands do not alter hard newlines and do not move words
across them. However, this property takes effect only if the
use-hard-newlines minor mode is enabled. See Hard and Soft Newlines in The GNU Emacs Manual.
This property specifies an extra right margin for filling this part of the text.
This property specifies an extra left margin for filling this part of the text.
This property specifies the style of justification for filling this part of the text.