Answer by michal.h21 for Highlight every occurrence of a list of words?

Solution using LuaTeX callbacks. Library luacolor.lua from luacolor is also used.

First package luahighlight.sty:

\ProvidesPackage{luahighlight}%\RequirePackage{luacolor}\@ifpackageloaded{xcolor}{}{\RequirePackage{xcolor}}\RequirePackage{luatexbase}\RequirePackage{luacode}\newluatexattribute\luahighlight\begin{luacode*}highlight = require "highlight"luatexbase.add_to_callback("pre_linebreak_filter", highlight.callback, "higlight")\end{luacode*}\newcommand\highlight[2][red]{  \bgroup  \color{#1}  \luaexec{highlight.add_word("\luatexluaescapestring{\current@color}","\luatexluaescapestring{#2}")}  \egroup}% save default document color\luaexec{highlight.default_color("\luatexluaescapestring{\current@color}")}% Use new attribute register in \set@color\protected\def\set@color{%  \setattribute\luahighlight{%    \directlua{%      oberdiek.luacolor.get("\luaescapestring{\current@color}")%    }%  }% \aftergroup\reset@color}% stolen from luacolor.sty\def\reset@color{}\def\luacolorProcessBox#1{%  \directlua{%    oberdiek.luacolor.process(\number#1)%  }%}\directlua{%  if luatexbase.callbacktypes.pre_shipout_filter then    token.get_next()  end}\@secondoftwo\@gobble{  \RequirePackage{atbegshi}[2011/01/30]  \AtBeginShipout{%    \luacolorProcessBox\AtBeginShipoutBox  }}\endinput

command \highlight is provided, with one required and one optional parameters. required is highlighted word, optional is color. In pre_linebreak_filter callback, words are collected and when matched, color information is inserted.

Lua module, highlight.lua:

local M = {}require "luacolor"local words = {}local chars = {}-- get attribute allocation number and register it in luacolorlocal attribute = luatexbase.attributes.luahighlight-- local attribute = oberdiek.luacolor.getattributeoberdiek.luacolor.setattribute(attribute)-- make local version of luacolor.getlocal get_color = oberdiek.luacolor.getvalue-- we must save default colorlocal default_color function M.default_color(color)  default_color = get_color(color)endlocal utflower = unicode.utf8.lowerfunction M.add_word(color,w)  local w = utflower(w)  words[w] = colorendlocal utfchar = unicode.utf8.char-- we don't want to include punctationlocal stop = {}for _, x in ipairs {".",",","!","“","”","?"} do stop[x] = true endlocal glyph_id = node.id("glyph")local glue_id  = node.id("glue")function M.callback(head)  local curr_text = {}  local curr_nodes = {}  for n in node.traverse(head) do    if n.id == glyph_id then      local char = utfchar(n.char)      -- exclude punctation      if not stop[char] then         local lchar = chars[char] or utflower(char)        chars[char] = lchar        curr_text[#curr_text+1] = lchar         curr_nodes[#curr_nodes+1] = n      end      -- set default color      local current_color = node.has_attribute(n,attribute) or default_color      node.set_attribute(n, attribute,current_color)    elseif n.id == glue_id  then      local word = table.concat(curr_text)      curr_text = {}      local color = words[word]      if color then        print(word)        local colornumber = get_color(color)        for _, x in ipairs(curr_nodes) do          node.set_attribute(x,attribute,colornumber)        end      end      curr_nodes = {}    end  end  return headendreturn M

we use pre_linebreak_filter callback to traverse the node list, we collect the glyph nodes (id 37) in a table and when we find a glue node (id 10, mainly spaces), we construct a word from collected glyphs. We have some prohibited characters (such as punctuation), which we strip out. All characters are lowercased, so we can detect even words at the beginning of sentences etc.

When a word is matched, we set attribute field of word glyphs to value under which is related color saved in luacolor library. Attributed are new concept in LuaTeX, they enable to store information in nodes, which can be processed later, as in our case, because at the shipout time, ale pages are processed by the luacolor library and nodes are colored, depending on their luahighlight attribute.

\documentclass{article}\usepackage[]{xcolor}\usepackage{luahighlight}\usepackage{lipsum}\highlight[red]{Lorem}\highlight[green]{dolor}\highlight[orange]{world}\highlight[blue]{Curabitur}\highlight[brown]{elit}\begin{document}\def\world{earth}\section{Hello world}Hello world, world? world! \textcolor{purple}{but normal colors works} too\footnote{And also footnotes, for instance. World WORLD wOrld}. Hello \world.\lipsum[1-12]\end{document}

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