+When writing an application that
+uses these string capabilities,
+the pairs should be first checked to see
+if each capability in the pair is set or only one is set:
+.bP
+If both \fBsmglp\fP and \fBsmgrp\fP are set,
+each is used with a single argument, \fIN\fP,
+that gives the column number of the left and right margin, respectively.
+.bP
+If both \fBsmgtp\fP and \fBsmgbp\fP are set,
+each is used to set the top and bottom margin,
+respectively:
+.RS 4
+.bP
+\fBsmgtp\fP is used with a single argument, \fIN\fP,
+the line number of the top margin.
+.bP
+\fBsmgbp\fP is used with two arguments, \fIN\fP and \fIM\fP,
+that give the line number of the bottom margin,
+the first counting from the top of the
+page and the second counting from the bottom.
+This accommodates the two styles of specifying
+the bottom margin in different manufacturers' printers.
+.RE
+.IP
+When designing a terminfo entry for a
+printer that has a settable bottom margin,
+only the first or second argument should be used, depending on the printer.
+When developing an application that uses \fBsmgbp\fP to set the bottom margin,
+both arguments must be given.
+.PP
+Conversely, when only one capability in the pair is set:
+.bP
+If only one of \fBsmglp\fP and \fBsmgrp\fP is set,
+then it is used with two arguments,
+the column number of the left and right margins, in that order.
+.bP
+Likewise, if only one of \fBsmgtp\fP and \fBsmgbp\fP is set, then it
+is used with two arguments that give the top and bottom margins,
+in that order, counting from the top of the page.
+.IP
+When designing a terminfo entry for a printer that requires setting both
+left and right or top and bottom margins simultaneously,
+only one capability in the pairs
+\fBsmglp\fP and \fBsmgrp\fP or
+\fBsmgtp\fP and \fBsmgbp\fP should be defined,
+leaving the other unset.
+.PP
+Except for very old terminal descriptions, e.g., those developed for SVr4,
+the scheme just described should be considered obsolete.
+An improved set of capabilities was added late in the SVr4 releases
+(\fBsmglr\fP and \fBsmgtb\fP),
+which explicitly use two parameters for setting the left/right or top/bottom
+margins.
+.PP
+When setting margins, the line- and column-values are zero-based.
+.PP
+The \fBmgc\fP string capability should be defined.
+Applications such as \fBtabs\fP(1) rely upon this to reset all margins.
+.\"
+.SS "Area Clears"