On the off chance that someone else may be interested, here is a lua filter 
that works by combining your walk_block filter with the one mentioned in 
this forum by EBkysko (link) 
<https://groups.google.com/g/pandoc-discuss/c/RyX2czqyZ10/m/EltdkHShAwAJ>. 
As written above, your filter can work for a single string, e.g. the 
surname, because in the AST the initials and in-between space are separate 
strings.  The modified version below gets the surname and initials (Smith, 
J.) underlined in the references:

``````lua
local underline_author_filter = {
  Para = function(el)
    if el.t == "Para" then
    for k,_ in ipairs(el.content) do
      if el.content[k].t == "Str" and el.content[k].text == "Smith,"
      and el.content[k+1].t == "Space"
      and el.content[k+2].t == "Str" and el.content[k+2].text:find("^J.") 
then
          local _,e = el.content[k+2].text:find("^J.")
          local rest = el.content[k+2].text:sub(e+1) 
          el.content[k] = pandoc.Underline { pandoc.Str("Smith, J.") }
          el.content[k+1] = pandoc.Str(rest)
          table.remove(el.content, k+2) 
      end
    end
  end
  return el
  end
}

function Div (div)
  if 'refs' == div.identifier then
    return pandoc.walk_block(div, underline_author_filter)
  end
  return nil
end
``````


 
On Monday, 23 November 2020 at 21:37:37 UTC+2 BP wrote:

> To traverse only the contents of a specific div in a Lua filter you want 
> to use the pandoc.walk_block function, something like this:
>
> ``````lua
> local underline_author_filter = {
>   Str = function (str)
>     if 'A. U. Thor' == str.text then
>       return pandoc.Underline(str)
>     end
>     return nil
>   end
> }
>
> function Div (div)
>   if 'refs' == div.identifier then
>     return pandoc.walk_block(div, underline_author_filter)
>   end
>   return nil
> end
> ``````
>
> -- 
> Better --help|less than helpless
>
> Den mån 23 nov. 2020 16:39gnpan <g.pan...-Re5JQEeQqe8AvxtiuMwx3w@public.gmane.org> skrev:
>
>> Thanks for the quick reply. I ended up creating a .json file, then a 
>> global find & replace in that, and then converted it to pdf. Works fine. I 
>> also had a go with a simple lua filter, but it only worked for strings in 
>> the body text, not the bibliography - not sure how to make it work for the 
>> bibliography div. 
>>
>> On Sunday, 22 November 2020 at 23:21:49 UTC+2 John MacFarlane wrote:
>>
>>>
>>> The citeproc library doesn't allow any formatting in given names, 
>>> so this bit of formatting is lost. 
>>>
>>> I'm not too tempted to change this. For things like 
>>> initialization, it's very convenient to have plain strings 
>>> here. 
>>>
>>> I would suggest using a lua filter which operates on the 
>>> bibliography Div and runs after the citeproc phase. 
>>> It can just find Str elements with your name and put 
>>> them in an Underline. 
>>>
>>>
>>> gnpan <g.pan...-Re5JQEeQqe8AvxtiuMwx3w@public.gmane.org> writes: 
>>>
>>> > In versions previous to 2.11 (latest was 2.10.1) I could highlight 
>>> only my 
>>> > name in reference lists (e.g. for cv) using the trick shown here 
>>> > 
>>> https://tex.stackexchange.com/questions/18664/underline-my-name-in-the-bibliography, 
>>>
>>> > which involves modifying my name in the .bib file and adding a 
>>> \newcommand 
>>> > under header-includes in the .txt file (see files below for MWE). This 
>>> does 
>>> > not work in subsequent pandoc versions and I assume it is an issue of 
>>> > citeproc vs. pandoc-citeproc. 
>>> > 
>>> > MWE (note that the default templates that came with each version have 
>>> to be 
>>> > used to avoid cslreference errors): 
>>> > For v.2.11.2: 
>>> > pandoc --pdf-engine=xelatex --citeproc --bibliography=test.bib 
>>> > --csl=nature.csl -o test11.pdf test.txt 
>>> > 
>>> > For v.2.10.1: 
>>> > pandoc --pdf-engine=xelatex --bibliography=test.bib --csl=nature.csl 
>>> -o 
>>> > test10.pdf test.txt 
>>> > Files: 
>>> > 1. test.txt contents: 
>>> > --- 
>>> > header-includes: 
>>> > - \newcommand{\myname}[1]{\textbf{First, A.}} 
>>> > --- 
>>> > 
>>> > Test [@first_test_2020] 
>>> > 
>>> > 2. test.bib file contents: 
>>> > @Article{first_test_2020, 
>>> > title = {Test title}, 
>>> > journaltitle = {Journal}, 
>>> > author = {{\myname{first}} and Second, B. and Third, C.}, 
>>> > date = {2020} 
>>> > } 
>>> > 
>>> > 3. nature.csl: https://www.zotero.org/styles?q=nature 
>>> > 4. Result with 2.10: test10.pdf 
>>> > <https://github.com/jgm/pandoc/files/5559278/test10.pdf> 
>>> > 5. Result with 2.11: test11.pdf 
>>> > <https://github.com/jgm/pandoc/files/5559279/test11.pdf> 
>>> > 
>>> > Sorry for cross-posting this from the github site (#6856), not sure 
>>> which 
>>> > is more appropriate. 
>>> > Thanks 
>>> > George 
>>> > 
>>> > -- 
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>>> https://groups.google.com/d/msgid/pandoc-discuss/ce795365-1926-49ca-947d-2dac0fa75f43n%40googlegroups.com. 
>>>
>>>
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>>
> To view this discussion on the web visit 
>> https://groups.google.com/d/msgid/pandoc-discuss/7aab780f-2a4e-4641-bc69-adc88280730an%40googlegroups.com 
>> <https://groups.google.com/d/msgid/pandoc-discuss/7aab780f-2a4e-4641-bc69-adc88280730an%40googlegroups.com?utm_medium=email&utm_source=footer>
>> .
>>
>

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