(k)sh.1: invocation-related edits for clarity and completeness

src/cmd/ksh93/sh.1

@@ -3940,8 +3940,8 @@ redefined for each instance.
 .PP
 When a type is defined a special built-in command of that name
 is added.  These built-ins are declaration commands and follow the
-same expansion rules as all the special built-in commands defined
-below that are preceded by \(dg\(dg.  These commands can subsequently
+same expansion rules as the built-in commands described below
+that are marked with a \(dd symbol. These commands can subsequently
 be used inside further type definitions.  The man page for these commands can
 be generated by using the
 .B \-\-man
@@ -7054,7 +7054,7 @@ to fail or zero if no command has failed.
 .TP 8
 .B posix
 Enable full POSIX standard compliance mode. This option
-is on by default if ksh is invoked as \fBsh\fR. It
+is on by default if ksh is invoked as \fBsh\fR, \fBrsh\fR, or \fBpfsh\fR. It
 disables passing exported variables' attributes (such as integer or readonly) to a new ksh process through the environment,
 causes file descriptors > 2 to be left open when invoking another program,
 makes the \fB<>\fR redirection operator default to standard input,
@@ -8046,14 +8046,48 @@ all interpretations of the given name to be reported.
 .SS Invocation.
 If the shell is invoked by
 .IR exec (2),
-and the first character of argument zero
+initialization depends on argument zero
 .RB ( $0 )
+as follows.
+If the first character of
+.B $0
 is
 .BR \- ,
+or the
+.B \-l
+option is given on the invocation command line,
 then the shell is assumed to be a
 .I login
-shell and
-commands are read from
+shell.
+If the basename of the command path in
+.B $0
+is
+.BR rsh ,
+.BR rksh ,
+or
+.BR krsh ,
+then the shell becomes restricted.
+If it is
+.BR pfsh
+or
+.BR pfksh ,
+then the shell becomes a profile shell (see
+.IR pfexec (1)).
+If the basename is
+.BR sh ,
+.BR rsh ,
+or
+.BR pfsh ,
+or the
+.B \-o\ posix
+option is given on the invocation command line, then
+the shell is initialized in full POSIX compliance mode
+(see the
+.B set
+builtin command above for more information).
+After this, if the shell was assumed to be a
+.I login
+shell, commands are read from
 .B /etc/profile
 and then from either
 .B .profile
@@ -8062,12 +8096,12 @@ in the current directory or
 if either file exists.
 Next, for interactive shells, commands are read from
 the file named by
-performing parameter expansion, command substitution,
-and arithmetic substitution on
-the value of the environment variable
 .SM
 .B ENV
-if the file exists.
+if the file exists, its name being determined by
+performing parameter expansion, command substitution,
+and arithmetic substitution on
+the value of that environment variable.
 If the
 .B \-s
 option is not present and