Fix invalid html in longtable captions
https://puszcza.gnu.org.ua/bugs/?315
https://bugs.gentoo.org/963668

commit 771081cac0d63632e67730e530eb8937271a68d9
Author: Michal Hoftich <michal.h21@gmail.com>
Date:   Wed Oct 1 14:56:02 2025 +0200

    added tablecaption dom filter

--- /dev/null
+++ b/texmf-dist/scripts/make4ht/domfilters/make4ht-tablecaption.lua
@@ -0,0 +1,25 @@
+local function get_parent_table(caption)
+  -- recursively find the parent table of a caption element, as it can be inside <tr> and <td>
+  local parent = caption:get_parent()
+  if parent and parent:get_element_name() == "table" then
+    return parent
+  elseif parent then
+    return get_parent_table(parent)
+  else
+    return nil
+  end
+end
+
+return function(dom)
+  -- the caption element must be a first element in table, it cannot be contained inside tr
+  for _, caption in ipairs(dom:query_selector("table caption")) do
+    local table = get_parent_table(caption)
+    if table then
+      -- insert caption as the first child of table
+      table:add_child_node(caption:copy_node(),1)
+      -- remove the original caption
+      caption:remove_node()
+    end
+  end
+  return dom
+end
--- a/texmf-dist/scripts/make4ht/extensions/make4ht-ext-common_domfilters.lua
+++ b/texmf-dist/scripts/make4ht/extensions/make4ht-ext-common_domfilters.lua
@@ -26,7 +26,7 @@ function M.modify_build(make)
     make:match("4om$", process, {charclasses= charclasses})
     count = 2
   else
-    local process = filter({"fixinlines", "idcolons", "joincharacters", "mathmlfixes", "tablerows","booktabs", "sectionid", "itemparagraphs"}, "commondomfilters")
+    local process = filter({"fixinlines", "idcolons", "joincharacters", "tablecaption", "mathmlfixes", "tablerows","booktabs", "sectionid", "itemparagraphs"}, "commondomfilters")
     make:match("html?$", process)
     count = 1
   end