These text properties affect the behavior of the fill commands. They are used for representing formatted text. See Filling, and Margins.

hard: 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.
right-margin: This property specifies an extra right margin for filling this part of the text.
left-margin: This property specifies an extra left margin for filling this part of the text.
justification: This property specifies the style of justification for filling this part of the text.