The FILL (abbreviated FIL) command reformats a block of text so that
there are as many full words on a line as possible without exceeding the
right margin.

Format: FILL [range]

The lines in the range must be contiguous.  If you omit the range, the
select range is assumed.

The right margin can be set by the SET WRAP command.  If the margin has
not been set, the default is the terminal width minus 1.