@Section
   @Title { "@HShift" and "@VShift" }
   @Tag { hshift }
@Begin
@PP
The @@HShift symbol
hshift.sym @Index { @@HShift symbol }
returns its right parameter with principal mark shifted as prescribed
by its left parameter:
@IL

@LI {
2i @Wide { |1rt @Code + & @I length @@HShift @I object }
|2m Principal mark shifted to the right by {@I length};
}

@LI {
2i @Wide { |1rt @Code - & @I length @@HShift @I object }
|2m Principal mark shifted to the left by {@I length};
}

@LI {
2i @Wide { |1rt @I length @@HShift @I object }
|2m Principal mark shifted so as to lie @I length to the right
of the left edge of {@I object};
}

@EL
In each chase @@HShift includes a @@OneCol effect.
@PP
The units of measurement of @I length may be {@Code "c"}, {@Code "i"},
{@Code "p"}, {@Code "m"}, {@Code "f"}, {@Code "s"}, {@Code "v"}, or
{@Code "w"}.  In the latter case, @Code "1w" is taken to be the width
of the right parameter, so that, for example, @Code "0.5w @HShift" will
centre the principal column mark within the right parameter.
@PP
vshift.sym @Index { @@VShift symbol }
The @@VShift symbol is similar except that it applies vertically to the
principal row mark:  @Code + & @I length shifts it down, @Code - & @I
length shifts it up, and @I length shifts it to @I length below the top
edge of the object.  With @@VShift, @Code "1w" is taken to be the height
of the right parameter.
@End @Section