a non-negative integer, or nil
.
nil
.
If it is non-nil, it specifies the right margin (as integer number of ems) to use when the pretty printer is making layout decisions.
If it is nil
, the right margin is taken to be the maximum line length
such that output can be displayed without wraparound or truncation.
If this cannot be determined, an implementation-dependent value is used.
This measure is in units of ems in order to be compatible with implementation-defined variable-width fonts while still not requiring the language to provide support for fonts.