Support \phantom and friends

luamml-kernel.lua

@@ -0,0 +1,42 @@
+local properties = node.get_properties_table()
+local if_vertical = token.create'ifv@'
+local if_horizontal = token.create'ifh@'
+local iftrue_index = token.create'iftrue'.index
+
+local funcid = luatexbase.new_luafunction'__luamml_kernel_finalize_phantom:N'
+token.set_lua('__luamml_kernel_finalize_phantom:N', funcid, 'protected')
+lua.get_functions_table()[funcid] = function()
+  -- TODO: Error handling etc
+  -- At this point, box 0 contains the inner expression and the curent list ends with the noad whose nucleus should get replaced
+  local size = token.scan_int()//2
+  local boxnum = 0
+  local startmath = tex.box[boxnum].list
+  assert(startmath.id == node.id"math")
+  local nucl = assert(tex.nest.top.tail.nucleus)
+  local props = properties[nucl]
+  if not props then -- very likely
+    props = {}
+    properties[nucl] = props
+  end
+  assert(not props.mathml_table)
+  local saved = assert(assert(properties[startmath]).saved_mathml_table)
+  if saved[0] == 'mstyle'
+      and (not saved.displaystyle or saved.displaystyle == (size == 0))
+      and (not saved.scriptlevel or saved.scriptlevel == (size == 0 and 0 or size-1))
+      then
+    saved[0], saved.displaystyle, saved.scriptlevel = 'mphantom', nil, nil
+  elseif saved[0] == 'mrow' then
+    saved[0] = 'mphantom'
+  else
+    saved = {[0] = 'mphantom', saved}
+  end
+  -- The following could be optimized for the case that both if_vertical and if_horizontal
+  -- are set, but that should't happen ayway and is just supported for consistency.
+  if if_vertical.index ~= iftrue_index then
+    saved = {[0] = 'mpadded', height = 0, depth = 0, saved}
+  end
+  if if_horizontal.index ~= iftrue_index then
+    saved = {[0] = 'mpadded', width = 0, saved}
+  end
+  props.mathml_table = saved
+end

luamml-patches-kernel.sty

@@ -0,0 +1,16 @@
+\ProvidesExplPackage {luamml-patches-kernel} {2021-05-30} {0.0.1-alpha}
+  {Feel free to add a description here}
+
+\lua_now:n { require'luamml-kernel' }
+
+\cs_set:Npn \mathph@nt #1 #2 {
+  \hbox_set:Nn \c_zero_int {
+    $
+    \m@th
+    #1
+    {#2}
+    $
+  }
+  \finph@nt
+  \__luamml_kernel_finalize_phantom:N #1
+}

luamml.sty

@@ -35,5 +35,6 @@
     \RequirePackage { luamml-patches-#1 }
   }
 }
+\RequirePackage { luamml-patches-kernel }
 \__luamml_patch_package:n {amsmath}
 \__luamml_patch_package:n {array}