mdocml: Sync man.7's LANGUAGE SYNTAX (was INPUT ENCODING) with mdoc.7.

[kristaps@mdocml.bsd.lv]

Log Message:
-----------
Sync man.7's LANGUAGE SYNTAX (was INPUT ENCODING) with mdoc.7.
While here, fix the scaling widths example that incorrectly used `br'
(it now correctly uses `sp').

Modified Files:
--------------
    mdocml:
        man.7

Revision Data
-------------
Index: man.7
===================================================================
RCS file: /usr/vhosts/mdocml.bsd.lv/cvs/mdocml/man.7,v
retrieving revision 1.102
retrieving revision 1.103
diff -Lman.7 -Lman.7 -u -p -r1.102 -r1.103
--- man.7
+++ man.7
@@ -49,28 +49,33 @@ prior macros:
 \&.SH Macro lines change control state.
 Other lines are interpreted within the current state.
 .Ed
-.Sh INPUT ENCODING
+.Sh LANGUAGE SYNTAX
 .Nm
 documents may contain only graphable 7-bit ASCII characters, the
 space character, and the tab character.
-.Pp
-Blank lines are acceptable; where found, the output will assert a
-vertical space.
-.Pp
-If the first character of a line is a space, that line is printed
-with a leading newline.
+The back-space character
+.Sq \e
+indicates the start of an escape sequence for
+.Sx Comments ,
+.Sx Predefined Strings ,
+and
+.Sx Special Characters .
 .Ss Comments
-Text following a
+Text following an escaped double-quote
 .Sq \e\*q ,
-whether in a macro or free-form text line, is ignored to the end of
+whether in a macro or text line, is ignored to the end of
 line.
-A macro line with only a control character and comment escape,
-.Sq \&.\e\*q ,
+A macro line beginning with a control character and comment escape
+.Sq \&.\e\*q
 is also ignored.
-Macro lines with only a control character and optionally whitespace are
+Furthermore,
+macro lines with only a control character and optional trailing
+whitespace are
 stripped from input.
 .Ss Special Characters
-Special characters may occur in both macro and free-form lines.
+Special characters are used to encode special glyphs and are rendered
+differently across output media.
+They may occur in both macro and text lines.
 Sequences begin with the escape character
 .Sq \e
 followed by either an open-parenthesis
@@ -79,25 +84,25 @@ for two-character sequences; an open-bra
 .Sq \&[
 for n-character sequences (terminated at a close-bracket
 .Sq \&] ) ;
-or a single one-character sequence.
+or a single one character sequence.
+.Pp
+Examples:
+.Bl -tag -width Ds -offset indent -compact
+.It \e(em
+em dash
+.It \ee
+backslash
+.El
+.Pp
 See
 .Xr mandoc_char 7
 for a complete list.
-Examples include
-.Sq \e(em
-.Pq em-dash
-and
-.Sq \ee
-.Pq back-slash .
 .Ss Text Decoration
 Terms may be text-decorated using the
 .Sq \ef
-escape followed by an indicator: B (bold), I (italic), R (Roman), or P
+escape followed by an indicator: B (bold), I (italic), R (regular), or P
 (revert to previous mode):
-.Pp
-.D1 \efBbold\efR \efIitalic\efP
-.Pp
-A numerical representation 3, 2, or 1 (bold, italic, and Roman,
+A numerical representation 3, 2, or 1 (bold, italic, and regular,
 respectively) may be used instead.
 A text decoration is only valid, if specified in free-form text, until
 the next macro invocation; if specified within a macro, it's only valid
@@ -109,26 +114,80 @@ open and close a font scope with each ar
 The
 .Sq \ef
 attribute is forgotten when entering or exiting a macro block.
+.Pp
+Examples:
+.Bl -tag -width Ds -offset indent -compact
+.It \efBbold\efR
+write in bold, then switch to regular
+.It \efIitalic\efP
+write in italic, then return to previous
+.El
+.Ss Predefined Strings
+Predefined strings, like
+.Sx Special Characters ,
+mark special output glyphs.
+Predefined strings are escaped with the slash-asterisk,
+.Sq \e* :
+single-character
+.Sq \e*X ,
+two-character
+.Sq \e*(XX ,
+and N-character
+.Sq \e*[N] .
+.Pp
+Examples:
+.Bl -tag -width Ds -offset indent -compact
+.It \e*(Am
+ampersand
+.It \e*(Ba
+vertical bar
+.El
+.Pp
+These strings are set using
+.Xr roff 7 ,
+although
+.Nm
+consists of several pre-set escapes listed in
+.Xr mandoc_char 7 .
 .Ss Whitespace
 Whitespace consists of the space character.
-In free-form lines, whitespace is preserved within a line; unescaped
-trailing spaces are stripped from input (unless in a literal context).
-Blank free-form lines, which may include spaces, are permitted and
-rendered as an empty line.
-.Pp
+In text lines, whitespace is preserved within a line.
 In macro lines, whitespace delimits arguments and is discarded.
-If arguments are quoted, whitespace within the quotes is retained.
-.Ss Scaling Widths
-Many macros support scaled widths for their arguments, such as
-stipulating a two-inch paragraph indentation with the following:
-.Bd -literal -offset indent
-\&.HP 2i
-.Ed
 .Pp
-The syntax for scaled widths is
-.Sq Li [+-]?[0-9]*.[0-9]*[:unit:]? ,
+Unescaped trailing spaces are stripped from text line input unless in a
+literal context.
+In general, trailing whitespace on any input line is discouraged for
+reasons of 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
+If the first character of a text line is a space, that line is printed
+with a leading newline.
+.Ss Quotation
+Macro arguments may be quoted with double-quotes; in this case,
+whitespace within the quotes is retained as part of the argument.
+.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.
+.Pp
+In text lines, quotes are regarded as opaque text.
+.Ss Scaling Widths
+Many macros support scaled widths for their arguments.
+The syntax for a scaled width is
+.Sq Li [+-]?[0-9]*.[0-9]*[:unit:] ,
 where a decimal must be preceded or proceeded by at least one digit.
 Negative numbers, while accepted, are truncated to zero.
+.Pp
 The following scaling units are accepted:
 .Pp
 .Bl -tag -width Ds -offset indent -compact
@@ -168,6 +227,8 @@ Using anything other than
 or
 .Sq v
 is necessarily non-portable across output media.
+See
+.Sx COMPATIBILITY .
 .Pp
 If a scaling unit is not provided, the numerical value is interpreted
 under the default rules of
@@ -175,15 +236,19 @@ under the default rules of
 for vertical spaces and
 .Sq u
 for horizontal ones.
-.Em Note :
-this differs from
-.Xr mdoc 7 ,
-which, if a unit is not provided, will instead interpret the string as
-literal text.
+.Pp
+Examples:
+.Bl -tag -width Ds -offset indent -compact
+.It \&.HP 2i
+two-inch tagged list indentation
+.Pq see Sx \&HP
+.It \&.sp 2v
+two vertical spaces
+.Pq see Sx \&sp
+.El
 .Ss Sentence Spacing
-When composing a manual, make sure that sentences end at the end of
-a line.
-By doing so, front-ends will be able to apply the proper amount of
+Sentences should terminate at the end of an input line.
+By doing this, a formatter will be able to apply the proper amount of
 spacing after the end of sentence (unescaped) period, exclamation mark,
 or question mark followed by zero or more non-sentence closing
 delimiters
@@ -193,6 +258,13 @@ delimiters
 .Sq \&' ,
 .Sq \&"
 .Pc .
+.Pp
+Examples:
+.Bd -literal -offset indent -compact
+Do not end sentences mid-line like this.  Instead,
+end a sentence like this.
+A new sentence gets a new line.
+.Ed
 .Sh MANUAL STRUCTURE
 Each
 .Nm
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