use Unicode characters for MathML font styles

CHANGELOG.md

@@ -1,5 +1,10 @@
 # Changelog
 
+- 2025/01/06
+
+  - use Unicode characters for MathML font styles.
+    https://tex.stackexchange.com/a/734331/2891
+
 - 2024/12/23 
 
   - fixed bug in the `make4ht-indexing` library. It didn't handle index entries

domfilters/make4ht-mathmlfixes.lua

@@ -1,4 +1,7 @@
 local log = logging.new("mathmlfixes")
+
+local mathml_chardata = require "make4ht-mathml-char-def"
+
 -- <mglyph> should be inside <mi>, so we don't process it 
 -- even though it is  a token element
 local token = {"mi", "mn", "mo", "mtext", "mspace", "ms"}
@@ -487,6 +490,41 @@ local function fix_rel_mo(el)
 
 end
 
+local uchar = utf8.char
+local ucodes = utf8.codes
+
+-- current version of MathML doesn't support the mathvariant attribute, so we need to replace unicode characters with the corresponding base code for the current font style
+local function replace_characters(math, current_style)
+  -- recursively loop over all the children of the math element and replace the unicode characters with the corresponding base code for the current font style
+  for _, child in ipairs(math:get_children()) do
+    if child:is_text() then
+      local text = child:get_text()
+      local new_text = {}
+      for _ ,char in ucodes(text) do
+        -- replace the unicode characters with the corresponding base code for the current font style
+        local code = mathml_chardata[char]
+        if code then
+          local new_char = code[current_style] or char
+          table.insert(new_text, uchar(new_char))
+        else
+          table.insert(new_text, uchar(char))
+        end
+      end
+      child._text = table.concat(new_text)
+    elseif child:is_element() then
+      local current_style = child:get_attribute("mathvariant") or current_style
+      replace_characters(child, current_style)
+    end
+  end
+end
+
+local function fix_mathml_chars(el)
+  local el_name, _ = get_element_name(el)
+  if el_name == "math" then
+    replace_characters(el, "normal")
+  end
+end
+
 
 return function(dom)
   dom:traverse_elements(function(el)
@@ -504,6 +542,10 @@ return function(dom)
     fix_numbers(el)
     fix_operators(el)
     fix_mathvariant(el)
+    if settings.output_format ~= "odt" then
+      -- ODT needs older MathML version
+      fix_mathml_chars(el)
+    end
     fix_dcases(el)
     top_mrow(el)
     delete_last_empty_mtr(el)