+.SS Margins
+SVr4 (and X/Open Curses)
+list several string capabilities for setting margins.
+Two were intended for use with terminals,
+and another six were intended for use with printers.
+.bP
+The two terminal capabilities assume that the terminal may have
+the capability of setting the left and/or right margin at the current
+cursor column position.
+.bP
+The printer capabilities assume that the printer may have
+two types of capability:
+.RS
+.bP
+the ability to set a top and/or bottom margin using the current
+line position, and
+.bP
+parameterized capabilities for setting the top, bottom, left, right margins
+given the number of rows or columns.
+.RE
+.PP
+In practice, the categorization into \*(``terminal\*('' and \*(``printer\*(''
+is not suitable:
+.bP
+The AT&T SVr4 terminal database uses \fBsmgl\fP four times,
+for AT&T hardware.
+.IP
+Three of the four are printers.
+They lack the ability to set left/right margins by specifying the column.
+.bP
+Other (non-AT&T) terminals may support margins
+but using different assumptions from AT&T.
+.IP
+For instance, the DEC VT420 supports left/right margins,
+but only using a column parameter.
+As an added complication, the VT420 uses two settings to fully enable
+left/right margins (left/right margin mode, and origin mode).
+The former enables the margins, which causes printed text
+to wrap within margins, but the latter is needed to prevent
+cursor-addressing outside those margins.
+.bP
+Both DEC VT420 left/right margins are set with a single control sequence.
+If either is omitted, the corresponding margin is set to the left or
+right edge of the display (rather than leaving the margin unmodified).
+.PP
+These are the margin-related capabilities:
+.PP
+.TS
+center;
+lb lb
+lb l .
+Name Description
+_
+smgl Set left margin at current column
+smgr Set right margin at current column
+smgb Set bottom margin at current line
+smgt Set top margin at current line
+smgbp Set bottom margin at line \fIN\fP
+smglp Set left margin at column \fIN\fP
+smgrp Set right margin at column \fIN\fP
+smgtp Set top margin at line \fIN\fP
+smglr Set both left and right margins to \fIL\fP and \fIR\fP
+smgtb Set both top and bottom margins to \fIT\fP and \fIB\fP
+.TE