5.20.2 Changing the Vertical Spacing

Request: .vs [space]

Request: .vs +space

Request: .vs -space

Register: \n[.v]

Set the vertical spacing to, or alter it by, space. The default scaling unit is ‘p’. If space is omitted, the formatter resets the vertical spacing to its previous value, or the default if there is none. If space is negative, the formatter sets the vertical spacing to the smallest possible positive value, the vertical motion quantum (as found in the .V register).²¹⁷

‘.vs 0’ isn’t saved in a diversion since it doesn’t result in a vertical motion.²¹⁸ You must explicitly issue this request before interpolating the diversion if you desire its effect.

The read-only register .v interpolates the vertical spacing.

When a break occurs, GNU troff performs the following procedure.

• Move the drawing position vertically by the extra pre-vertical line space, the minimum of all negative \x escape sequence arguments in the pending output line. If this motion springs a vertical position trap,²¹⁹ including the implicit page trap,²²⁰ interrupt this procedure.
• Move the drawing position vertically by the vertical line spacing. If this motion springs a trap, including the implicit page trap, interrupt this procedure.
• Apply any configured adjustment and marginal annotations²²¹, and append the pending output line to the current diversion²²² (often, the output device’s current page).
• Move the drawing position vertically by the extra post-vertical line space, the maximum of all positive \x escape sequence arguments in the line that has just been output. If this motion springs a trap, including the implicit page trap, abort this procedure.
• Move the drawing position vertically by the post-vertical line spacing (see below). If this motion springs a trap, including the implicit page trap, abort this procedure.

If the break procedure is interrupted or aborted because a vertical position trap is sprung, GNU troff updates the values of the .ne and .trunc registers.²²³ Encountering the implicit page trap (ibid.) does not alter them.

Prefer vs or pvs over ls to produce double-spaced documents. vs and pvs have finer granularity than ls; moreover, some preprocessors assume single spacing. Recall Manipulating Spacing, regarding the \x escape sequence and the ls request.

Request: .pvs [space]

Request: .pvs +space

Request: .pvs -space

Register: \n[.pvs]

Set the post-vertical spacing to, or alter it by, space. The default scaling unit is ‘p’. If pvs is invoked without an argument, the post-vertical spacing is reset to the previous value before the last call to pvs. GNU troff emits a warning in category ‘range’ if space is negative; the post-vertical spacing is then set to zero.

The read-only register .pvs interpolates the post-vertical spacing.