ConTeXt writer: new section syntax and --section-divs (#4295)

Fixes #2609.

This PR introduces the new-style section headings: `\section[my-header]{My Header}` -> `\section[title={My Header},reference={my-header}]`.

On top of this, the ConTeXt writer now supports the `--section-divs` option to write sections in the fenced style, with `\startsection` and `\stopsection`.

1 files changed, 35 insertions, 32 deletions

diff --git a/test/writer.context b/test/writer.context
index e7af684f8..0cbbc7df4 100644
--- a/test/writer.context
+++ b/test/writer.context
@@ -72,32 +72,34 @@ markdown test suite.
 
 \thinrule
 
-\section[headers]{Headers}
+\section[title={Headers},reference={headers}]
 
-\subsection[level-2-with-an-embedded-link]{Level 2 with an
-\useURL[url1][/url][][embedded link]\from[url1]}
+\subsection[title={Level 2 with an \useURL[url1][/url][][embedded
+link]\from[url1]},reference={level-2-with-an-embedded-link}]
 
-\subsubsection[level-3-with-emphasis]{Level 3 with {\em emphasis}}
+\subsubsection[title={Level 3 with
+{\em emphasis}},reference={level-3-with-emphasis}]
 
-\subsubsubsection[level-4]{Level 4}
+\subsubsubsection[title={Level 4},reference={level-4}]
 
-\subsubsubsubsection[level-5]{Level 5}
+\subsubsubsubsection[title={Level 5},reference={level-5}]
 
-\section[level-1]{Level 1}
+\section[title={Level 1},reference={level-1}]
 
-\subsection[level-2-with-emphasis]{Level 2 with {\em emphasis}}
+\subsection[title={Level 2 with
+{\em emphasis}},reference={level-2-with-emphasis}]
 
-\subsubsection[level-3]{Level 3}
+\subsubsection[title={Level 3},reference={level-3}]
 
 with no blank line
 
-\subsection[level-2]{Level 2}
+\subsection[title={Level 2},reference={level-2}]
 
 with no blank line
 
 \thinrule
 
-\section[paragraphs]{Paragraphs}
+\section[title={Paragraphs},reference={paragraphs}]
 
 Here's a regular paragraph.
 
@@ -112,7 +114,7 @@ here.
 
 \thinrule
 
-\section[block-quotes]{Block Quotes}
+\section[title={Block Quotes},reference={block-quotes}]
 
 E-mail style:
 
@@ -155,7 +157,7 @@ And a following paragraph.
 
 \thinrule
 
-\section[code-blocks]{Code Blocks}
+\section[title={Code Blocks},reference={code-blocks}]
 
 Code:
 
@@ -179,9 +181,9 @@ These should not be escaped:  \$ \\ \> \[ \{
 
 \thinrule
 
-\section[lists]{Lists}
+\section[title={Lists},reference={lists}]
 
-\subsection[unordered]{Unordered}
+\subsection[title={Unordered},reference={unordered}]
 
 Asterisks tight:
 
@@ -249,7 +251,7 @@ Minuses loose:
   Minus 3
 \stopitemize
 
-\subsection[ordered]{Ordered}
+\subsection[title={Ordered},reference={ordered}]
 
 Tight:
 
@@ -308,7 +310,7 @@ Multiple paragraphs:
   Item 3.
 \stopitemize
 
-\subsection[nested]{Nested}
+\subsection[title={Nested},reference={nested}]
 
 \startitemize[packed]
 \item
@@ -362,7 +364,7 @@ Same thing but with paragraphs:
   Third
 \stopitemize
 
-\subsection[tabs-and-spaces]{Tabs and spaces}
+\subsection[title={Tabs and spaces},reference={tabs-and-spaces}]
 
 \startitemize
 \item
@@ -378,7 +380,7 @@ Same thing but with paragraphs:
   \stopitemize
 \stopitemize
 
-\subsection[fancy-list-markers]{Fancy list markers}
+\subsection[title={Fancy list markers},reference={fancy-list-markers}]
 
 \startitemize[n][start=2,left=(,stopper=),width=2.0em]
 \item
@@ -442,7 +444,7 @@ B. Williams
 
 \thinrule
 
-\section[definition-lists]{Definition Lists}
+\section[title={Definition Lists},reference={definition-lists}]
 
 Tight using spaces:
 
@@ -553,7 +555,7 @@ Blank line after term, indented marker, alternate markers:
   \stopitemize
 \stopdescription
 
-\section[html-blocks]{HTML Blocks}
+\section[title={HTML Blocks},reference={html-blocks}]
 
 Simple block on one line:
 
@@ -613,7 +615,7 @@ Hr's:
 
 \thinrule
 
-\section[inline-markup]{Inline Markup}
+\section[title={Inline Markup},reference={inline-markup}]
 
 This is {\em emphasized}, and so {\em is this}.
 
@@ -642,7 +644,8 @@ spaces: a^b c^d, a\lettertilde{}b c\lettertilde{}d.
 
 \thinrule
 
-\section[smart-quotes-ellipses-dashes]{Smart quotes, ellipses, dashes}
+\section[title={Smart quotes, ellipses,
+dashes},reference={smart-quotes-ellipses-dashes}]
 
 \quotation{Hello,} said the spider. \quotation{\quote{Shelob} is my name.}
 
@@ -665,7 +668,7 @@ Ellipses\ldots{}and\ldots{}and\ldots{}.
 
 \thinrule
 
-\section[latex]{LaTeX}
+\section[title={LaTeX},reference={latex}]
 
 \startitemize[packed]
 \item
@@ -705,7 +708,7 @@ Here's a LaTeX table:
 
 \thinrule
 
-\section[special-characters]{Special Characters}
+\section[title={Special Characters},reference={special-characters}]
 
 Here is some unicode:
 
@@ -766,9 +769,9 @@ Minus: -
 
 \thinrule
 
-\section[links]{Links}
+\section[title={Links},reference={links}]
 
-\subsection[explicit]{Explicit}
+\subsection[title={Explicit},reference={explicit}]
 
 Just a \useURL[url4][/url/][][URL]\from[url4].
 
@@ -788,7 +791,7 @@ Just a \useURL[url4][/url/][][URL]\from[url4].
 
 \useURL[url12][][][Empty]\from[url12].
 
-\subsection[reference]{Reference}
+\subsection[title={Reference},reference={reference}]
 
 Foo \useURL[url13][/url/][][bar]\from[url13].
 
@@ -812,7 +815,7 @@ Foo \useURL[url19][/url/][][bar]\from[url19].
 
 Foo \useURL[url20][/url/][][biz]\from[url20].
 
-\subsection[with-ampersands]{With ampersands}
+\subsection[title={With ampersands},reference={with-ampersands}]
 
 Here's a \useURL[url21][http://example.com/?foo=1&bar=2][][link with an
 ampersand in the URL]\from[url21].
@@ -825,7 +828,7 @@ Here's an \useURL[url23][/script?foo=1&bar=2][][inline link]\from[url23].
 Here's an \useURL[url24][/script?foo=1&bar=2][][inline link in pointy
 braces]\from[url24].
 
-\subsection[autolinks]{Autolinks}
+\subsection[title={Autolinks},reference={autolinks}]
 
 With an ampersand: \useURL[url25][http://example.com/?foo=1&bar=2]\from[url25]
 
@@ -853,7 +856,7 @@ or here: <http://example.com/>
 
 \thinrule
 
-\section[images]{Images}
+\section[title={Images},reference={images}]
 
 From \quotation{Voyage dans la Lune} by Georges Melies (1902):
 
@@ -863,7 +866,7 @@ Here is a movie {\externalfigure[movie.jpg]} icon.
 
 \thinrule
 
-\section[footnotes]{Footnotes}
+\section[title={Footnotes},reference={footnotes}]
 
 Here is a footnote reference,\footnote{Here is the footnote. It can go
   anywhere after the footnote reference. It need not be placed at the end of