@Section
   @Title { "@YUnit" and "@ZUnit" }
   @Tag { yunit }
@Begin
@PP
The @@YUnit symbol
yunit.sym @Index { @@YUnit symbol }
zunit.sym @Index { @@ZUnit symbol }
changes the value of the @Code y unit of measurement (Section
{@NumberOf concatenation}) within its right parameter to the value
given by the left parameter:
@ID {
@Code "1c @YUnit { ..."
}
ensures that the value of @Code "1y" within the right parameter will
be {@Code "1c"}.  The @@ZUnit symbol is similar, setting the value
of the @Code z unit in its right parameter.  Both units have default
value zero.  The left parameter may not include a gap mode, nor may it
use the {@Code w}, {@Code b}, {@Code r}, or of course {@Code d} units,
but it may begin with @Code "+" or @Code "-" to indicate that value is
to be added to or subtracted from the current value.  Any negative result
of using @Code "-" will be silently replaced by zero.
@PP
These units are not used internally by Lout.  They are supplied as
part of the style information for the convenience of application
packages.  For example, the Eq equation formatting package uses them
to fine-tune the appearance of equations.
@End @Section
