path: root/doc/expert/pre_spac

@Section
   @Title { "@Space" }
   @Tag { space }
@Begin
@PP
The @@Space symbol
space.sym @Index { @@Space symbol }
changes the value of the @Code s unit of measurement (Section
s.unit.space @SubIndex { and @@Space symbol }
{@NumberOf concatenation}) within its right parameter to the value
given by the left parameter:
@ID {
@Code "1c @Space { a b c d }"
}
has result
@ID {
1c @Space { a b c d }
}
As for the @@Break symbol, the left parameter of @@Space may be given
relative to the enclosing @Code s unit, and it may include a gap
mode.  Note that the @@Font symbol also sets the @Code s unit.
@PP
The left parameter of the @@Space symbol may also hold any one of the
five special values {@Code lout}, {@Code compress}, {@Code separate},
{@Code troff}, and {@Code tex}, which control the way in which Lout
treats white space separating two objects.  The names {@Code troff}
and {@Code tex} indicate that the behaviour of these options is
inspired by these other document formatting systems.
@PP
The default setting, {@Code lout}, produces as many spaces in the output as
there are in the input.  The {@Code compress} setting causes all sequences
of two or more white space characters to be treated the same as one white
space character.  The {@Code separate} setting is like {@Code compress}
but also causes zero white spaces between two objects (but not within
one word) to be treated the same as one white space character.
@PP
The {@Code troff} setting is the same as {@Code lout} except that
wherever a sentence ends at the end of a line, one extra space is
added.  Formally, when two objects are separated by white space
characters which include at least one newline character, and the
first object is a word ending in any one of a certain set of
sequences of characters, the extra space is added.  The set of
sequences of characters depends on the current language and is defined
in the @Code langdef for that language (see Section {@NumberOf language}).
@PP
The {@Code tex} option is the most complicated.  First, the
{@Code compress} option is applied.  Then, at every sentence ending,
whether or not at the end of a line, one extra space is added.  A
sentence ending is defined as for {@Code troff} except that, in addition
to the preceding word having to end in one of a certain set of sequences of
characters, the character preceding that sequence must exist and must
be a lower-case letter.  A character is a lower-case letter if, in the
Lout Character Mapping file (Section {@NumberOf font}) associated with
the current font, an upper-case equivalent of the character is defined.
@End @Section