mdocml: Add some new text written from scratch after checking whether

[schwarze@mdocml.bsd.lv]

Log Message:
-----------
Add some new text written from scratch after checking whether anything
explained in mdoc.samples(7) is missing from mdoc(7):
* Discourage trailing whitespace.
* Move all information about quoted arguments to the relevant
  subsection, shortening it a bit, and adding an example.
* Mention that blanks can be quoted with a backslash.
* A better .Nd line in the template (verbatim from mdoc.samples(7)).
* Explain how to escape callable macro names, and provide examples.
ok jmc@

Modified Files:
--------------
    mdocml:
        mdoc.7

Revision Data
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Index: mdoc.7
===================================================================
RCS file: /usr/vhosts/mdocml.bsd.lv/cvs/mdocml/mdoc.7,v
retrieving revision 1.193
retrieving revision 1.194
diff -Lmdoc.7 -Lmdoc.7 -u -p -r1.193 -r1.194
--- mdoc.7
+++ mdoc.7
@@ -178,15 +178,38 @@ trailing spaces are stripped from input 
 Blank text lines, which may include whitespace, are only permitted
 within literal contexts.
 .Pp
+In general, trailing whitespace on input lines is discouraged
+for reasons of clarity and portability.
+In the rare case that a blank character is needed at the end of an
+input line, it may be forced by
+.Sq \e\ \e& .
+.Pp
 In macro lines, whitespace delimits arguments and is discarded.
-If arguments are quoted, whitespace within the quotes is retained.
 .Ss Quotation
-Macro arguments may be quoted with double-quotes to group
-space-delimited terms or to retain blocks of whitespace.
+Macro arguments may be quoted with double-quotes; in this case,
+whitespace within the quotes is retained as part of the argument.
+For example,
+.Pp
+.D1 Pf \. \&Fn strlen "\(dqconst char *s\(dq"
+.Pp
+renders as
+.Sq Fn strlen "const char *s" ,
+while
+.Pp
+.D1 Pf \. \&Fn strlen "const char *s"
+.Pp
+would produce
+.Sq Fn strlen const char *s .
+.Pp
 A quoted argument begins with a double-quote preceded by whitespace.
 The next double-quote not pairwise adjacent to another double-quote
 terminates the literal, regardless of surrounding whitespace.
 .Pp
+In unquoted arguments, space characters can alternatively be included
+by preceding them with a backslash
+.Pq Sq \e\~ ,
+but quoting is usually better for clarity.
+.Pp
 Note that any quoted text, even if it would cause a macro invocation
 when unquoted, is considered literal text.
 Thus, the following produces
@@ -304,7 +327,7 @@ file for a utility
 \&.Os
 \&.Sh NAME
 \&.Nm progname
-\&.Nd a description goes here
+\&.Nd one line about what it does
 \&.\e\*q .Sh LIBRARY
 \&.\e\*q For sections 2, 3, & 9 only.
 \&.\e\*q Not used in OpenBSD.
@@ -600,6 +623,17 @@ The
 .Em Callable
 column indicates that the macro may also be called by passing its name
 as an argument to another macro.
+For example,
+.Sq \&.Op \&Fl O \&Ar file
+produces
+.Sq Op Fl O Ar file .
+To prevent a macro call and render the macro name literally,
+escape it by prepending a non-breaking space,
+.Sq \e& .
+For example,
+.Sq \&Op \e&Fl O
+produces
+.Sq Op \&Fl O .
 If a macro is not callable but its name appears as an argument
 to another macro, it is interpreted as opaque text.
 For example,
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