@Section
   @Title { "@OneCol" and "@OneRow" }
   @Tag { onerow }
@Begin
@PP
The @@OneRow symbol
onerow.sym @Index { @@OneRow symbol }
principal.mark.effect @SubIndex { effect on @@OneCol and @@OneRow }
returns its right parameter modified so that only the principal row mark
protrudes.  This is normally the first row mark, but another one may be
chosen by preceding it with @Code "^/" or {@Code "^//"}.  For example,
@ID @Code {
"@OneRow {  |0.5rt  Slope @Font x + 2  ^//1p  @HLine  //1p  |0.5rt  5 }"
}
has result
@LP
@ID {
@ShowMarks
@OneRow { |0.5rt Slope @Font x + 2 ^//1p @HLine //1p |0.5rt 5 }
}
@LP
with one row mark protruding from the bar as shown.  Compare this with
@ID @Code {
"@OneRow {  |0.5rt  Slope @Font x + 2  //1p  @HLine  //1p  |0.5rt  5 }"
}
where the mark protrudes from the numerator:
@LP
@ID {
@ShowMarks
@OneRow { |0.5rt Slope @Font x + 2 //1p @HLine //1p |0.5rt 5 }
}
onecol.sym @Index { @@OneCol symbol }
@@OneCol has the same effect on columns as @@OneRow does on rows, with
the symbols @Code "^|" and @Code "^||" (or {@Code "^&"}) determining
which mark is chosen.
@End @Section