Verbatim-safe typography, ^-punctuation quoting, full-range ^UUUU^, polyglot html

Typographic transforms (---, quote pairs, ~) no longer touch verbatim
text: @c/@code/@source_listing content and ^'...'^ spans show exactly the
characters written. "^" before any punctuation character quotes it in
every target (the apostrophe excepted: ^' opens a literal span), with the
new :resolve option on @@@target declaring per-target renderings. The
^UUUU^ code-point form accepts 4-6 hex digits, the full Unicode range.
The html output and transform spellings are polyglot (XML-valid), in
preparation for an EPUB target. New suites: transform_test, character_test
(engine), typography_test (SKS).

(from dev 07ce5ea86a0a)

sks/target/target.k

@@ -15,10 +15,30 @@ The LaTeX transformations supported by the SKS are:
   ''   ->  close double quote
   ~    ->  non-breaking space
 
+"^" before any punctuation character quotes it (an engine rule, not an SKS
+one): the character reaches the output literally, taking no part in the
+transforms above -- ^-^- writes two plain hyphens (a --flag in prose), ^~ a
+plain tilde.  The one exception is the apostrophe: "^" before it opens a
+literal span instead (a literal apostrophe is ^0027^), and writing that
+pair even in THIS comment would open one -- the span sentinels are placed
+before text removal.  A target where the raw character would
+still be re-interpreted declares its rendering with :resolve -- the tex
+target maps a quoted hyphen to {-} (a bare -- in .tex re-forms TeX's dash
+ligature) and a quoted tilde to \textasciitilde{} (a raw ~ is TeX's
+non-breaking space).  Verbatim text (@c, @code, ^'...'^) never needs any
+of this: neither the transforms nor the quoting reach it.
+
 ]#
 
 
-@@@target txt | Plain text with formatting |  # This txt target is not full implemented in the SKS yet.
+@@@state Target_txt_width
+  :desc Width of the text in the plain text target (txt)
+  :value 72
+@@@
+
+
+# The txt target is not fully implemented in the SKS yet.
+@@@target txt | Plain text with formatting |  
   --  -  |
   --- -- |
   ``  "  |
@@ -27,24 +47,35 @@ The LaTeX transformations supported by the SKS are:
   '   '  |
   ~   ^0020^
   :after_apply
-    phases.justify_blocks
+    phases.txt_format_footnotes ;
+    phases.txt_justify_blocks
 @@@
 
 @@@target html | HTML page
 #  :escape < &lt; & &amp; |
 |
-  --- &mdash; |
-  -- &ndash;  |
+  --- &^#x2014; |
+  -- &^#x2013;  |
   `` “        |
   '' ”        |
   ` ‘         |
   ' ’         |
-  ^^~ &tilde; |
-  ~ &nbsp;
+  ~ &^#160;
+  :after_apply
+    phases.html_format_footnotes
 @@@
 
+# No transforms: LaTeX applies the input conventions itself.  The :resolve
+# entries say how a QUOTED character renders where the raw character would
+# still be re-interpreted by TeX: ^- resolves to {-}, not a bare -, or the
+# hyphens re-form a run and the dash ligature turns ^-^- into an en-dash;
+# ^~ resolves to \textasciitilde{}, since a raw ~ is TeX's non-breaking
+# space.  Other quoted punctuation either has an :escape entry (its marker
+# takes the escape replacement: ^$ renders as \$) or decodes to the raw
+# character.
 @@@target tex | LaTeX
-:escape \ \textbackslash{} & \& { \{ } \} $ \$ % \% _ \_ ^# \^# ^^ \textasciicircum{}
+  :escape \ \textbackslash{} & \& { \{ } \} $ \$ % \% _ \_ ^# \^# ^^ \textasciicircum{}
+  :resolve - {-} ~ \textasciitilde{}
 @@@
 
 @@@target pdf | PDF from LaTeX