Width and height argtypes, kdesc --argtypes from ref/, txt @define/@left_right/@columns, kdiag --check value validation (from dev d6993110e9b3)

Also: the klammertext argtype (descriptions kept as source), txt table
wrapping and :hpos/:offset, @c between ‹ ›, txt section headings, the
ktext newline-only trim, capitalize(), and the argtype test suite.

Co-Authored-By: Claude Fable 5.1 <noreply@anthropic.com>

sks/code/code_block.py

@@ -349,6 +349,18 @@ class Code_fragment(klammer_base.Klammer_base):
     def tex(self):
         return f"{{\\tt {tex_line(self.code_text.strip())}}}"
 
+    def txt(self):
+        # Plain text has no face to switch to: the fragment is its own text.
+        # As in html_line/tex_line, the Klammertext specials are quoted for
+        # the @eval read-back (a bare "@" in the result would be a klammer
+        # without a beginning) and the typographically active characters
+        # hidden, so a "--" in code stays two hyphens.
+        result = klammer_base.hide_typographic(quote_specials(self.code_text.strip()))
+        # Surround code symbols with ‹ and ›, though there are conflicts in Swiss
+        # German, Italian and some Scandinavian languages. Should be clear in
+        # context, though.
+        result = "\u2039" + result + "\u203A"
+        return result
 
 def extract_marked_region(src, marker, filename):
     """The region of `src` between two lines that are exactly "//<marker>".