Details about what can be supplied as an argument are contained in the description opposite each command. Conversely, an argument not enclosed in square brackets must be supplied whenever the command is used. An argument enclosed in square brackets and printed in boldface is optional, but, if used, must be typed literally as shown. First line is indented by the value of register PI, and following lines begin at the current main indentation level. No first-line indentation.
All lines begin at the main indentation level.
The entire block is left-adjusted and then, by default, indented the value of register PI to the right of the main indentation level. If one argument is given, it is a label to be placed at the main indentation level opposite the first line of the paragraph. Nonstandard indentation must be specified if the label is too wide to fit within the default indentation. This nonstandard indentation persists in subsequent .IPs in a series, disappearing when the series is ended by a return to some other format such as a section heading or a .PP or .LP paragraph. For nonstandard indentation without any label, the first argument should be simply a pair of double-quote marks with nothing between them.