Implement versioned themes

CHANGES.md

@@ -2,14 +2,29 @@
 
 ## 3.8.0
 
+Development:
+
+- Add support for versioned themes and add new Lua option `experimental`.
+  (#466, #512, #514, [matrix.org][matrix-514] reviewed by @TeXhackse, #521)
+
+  The option `experimental` enables experimental features that are planned to
+  be the new default in the next major release of the Markdown package.
+
+  At the moment, this just means that the version `experimental` of the theme
+  `witiko/markdown/defaults` will be loaded and warnings for hard-deprecated
+  features will become errors. However, the effects may extend to other areas
+  in the future as well.
+
+ [matrix-514]: https://matrix.to/#/!UeAwznpYwwsinVTetR:matrix.org/$TTc-m7B5NSdsLBNNyIuFWQ-u2nOZ03lJ5js88hnyFiU?via=matrix.org&via=im.f3l.de
+
 Documentation:
 
 - Document LaTeX hooks. (#464, #507)
 
 Defaults:
 
 - Improve the compatibility of the default LaTeX packages with PDF tagging:
-  (#466, #512, reported and consulted by @u-fischer)
+  (#466, #512, #514, #521, reported and consulted by @u-fischer)
 
   - In TeX engines other than LuaTeX, use the package soul instead of the
     package soulutf8 in TeX Live ≥ 2023.
@@ -18,8 +33,14 @@ Defaults:
     prototypes instead of the package soul.
 
   - Use the package enumitem for tight and fancy lists instead of the package
-    paralist. If you wish to keep using the package paralist, load it before
-    the Markdown package to force the old behavior.
+    paralist.
+
+    This is a breaking change that is marked as experimental. To enable it,
+    either use the package option `experimental` or specify any test phase in
+    the document metadata:
+
+    1. `\usepackage[experimental]{markdown}`
+    2. `\DocumentMetadata{testphase=phase-III}`
 
 Continuous Integration:
 

Makefile

@@ -20,8 +20,8 @@ EXAMPLES_SOURCES=examples/context-mkiv.tex \
   examples/optex.tex
 EXAMPLES=examples/context-mkiv.pdf \
   examples/latex-pdftex.pdf examples/latex-xetex.pdf examples/latex-luatex.pdf \
-  examples/latex-tex4ht.html examples/latex-tex4ht.css \
   examples/optex.pdf
+# examples/latex-tex4ht.html examples/latex-tex4ht.css
 TESTS=tests/test.sh tests/test.py tests/requirements.txt tests/support/*.tex \
   tests/templates/*/*/head.tex.m4 tests/templates/*/*/body.tex.m4 \
   tests/templates/*/*/foot.tex.m4 tests/templates/*/COMMANDS.m4 tests/testfiles/*/*/*.test

examples/Makefile

@@ -30,8 +30,8 @@ LUACLI_OPTIONS=\
 OUTPUT=\
   context-mkiv.pdf \
   latex-pdftex.pdf latex-xetex.pdf latex-luatex.pdf \
-  latex-tex4ht.html latex-tex4ht.css \
   optex.pdf
+# latex-tex4ht.html latex-tex4ht.css
 
 # This is the default pseudo-target.
 all: $(OUTPUT)