+The {parameter} escape is typically used in a command line argument
+that should only be present if it has a non-null value. Its value
+will be wrapped with single quotes if the escape is not so wrapped.
+Shell parameter expansion can construct the argument only when it is
+non-null, e.g.,
+.PP
+.RS 5
+.nf
+mhshow-show-text/html: charset=%{charset};
+ w3m ${charset:+-I $charset} -T text/html %F
+.fi
+.RE
+.PP
+That example also shows the use of indentation to signify continuation:
+the two text lines combine to form a single entry.
+.PP