Almost there. You need


`content = {pandoc.Str"Foo"}`


since the content of a Header is a list of inline elements.

As for multiple possible values Lua patterns are, as you seem to have
discovered, a bit challenged in that they don't support alternations. The
best solution is to use a table:

``````lua
-- Localize `pandoc` to a shorter name to save space & type less!
local p = pandoc

-- This is your "substitution" table.
local text4match = {
  -- If you need styling do this:
  foo = { p.Str"Foo", p.Space(), p.Str"and", p.Space(),
p.Emph(p.Str"more.") },
  -- If you do not need styling you can do this:
  bar = { p.Str"Bar and less." },
}

function RawBlock (elem)
  local key = elem.text:match"%<%!%-%-%s*(%a+)%s*%-%-%>"
  if key then
    local text = text4match[key]
    if text then
      return p.Header(2, text)
    end
  end
  -- No match, no text, ignore this elem
  return nil
end
``````

HTH,

/bpj

-- 
Better --help|less than helpless

Den fre 15 jan. 2021 04:39Peter Matulis <pmatulis-Re5JQEeQqe8AvxtiuMwx3w@public.gmane.org> skrev:

> So I now have this:
>
> function RawBlock(el)
>   if el.text:match("%<%!%-%- foo %-%-%>") then
>     content = "foo"
>     return pandoc.Header(2, content)
>   end
> end
>
> There are actually about a dozen such known Markdown comments (e.g. 'foo',
> 'bar').
> Instead of creating multiple files I'd like to have just one that uses a
> regex and capture group:
>
>   if el.text:match("%<%!%-%- (%a+) %-%-%>") then
>
> I'm just unsure how to refer to the capture in a conditional statement
> (i.e. "if 'foo' is captured then 'content' = "foo", elsif 'bar' is
> captured then 'content' = "bar").
>
>
> On Thu, 14 Jan 2021 at 15:57, Peter Matulis <pmatulis-Re5JQEeQqe8AvxtiuMwx3w@public.gmane.org> wrote:
>
>> Gratitude. This got me going.
>>
>> On Thu, 14 Jan 2021 at 13:52, John MacFarlane <jgm-TVLZxgkOlNX2fBVCVOL8/A@public.gmane.org> wrote:
>>
>>>
>>> What you want to do is match on a RawBlock element.
>>> Something like
>>>
>>> function RawBlock(el)
>>>   if el.text:match("<!--") then
>>>     content = -- fill this in based on el.text
>>>     return pandoc.Header(2, content)
>>>   end
>>> end
>>>
>>>
>>> Peter Matulis <pmatulis-Re5JQEeQqe8AvxtiuMwx3w@public.gmane.org> writes:
>>>
>>> > Hi. I'm new to Pandoc & Lua but my present issue is straightforward. I
>>> am
>>> > converting a Markdown file to HTML with pandoc like this:
>>> >
>>> > pandoc -L filter.lua -f gfm -t html -o file.html file.md
>>> >
>>> > Where file.md contains a line with this MD comment (the MD file was
>>> > obtained by converting from RST where I had to seed that file with an
>>> RST
>>> > comment to use as a placeholder for what I'm doing here):
>>> >
>>> > <!-- blah -->
>>> >
>>> > I simply want to convert this into an actual (second-level) MD header:
>>> >
>>> > ## blah
>>> >
>>> > From what I've read, I would ideally specify an "element" that will be
>>> > acted upon, but what is a comment considered? Anyway, I think I can
>>> specify
>>> > `Pandoc` to mean "check the entire document", and that's what I've done
>>> > here (I will eventually be iterating through multiple MD files so I
>>> should
>>> > really not be doing it like this; please advise!):
>>> >
>>> > function Pandoc (value)
>>> >   comment = "<!-- blah -->"
>>> >   comment = comment:gsub("%<%!%-%- blah %-%-%>", "## blah")
>>> >   return value
>>> > end
>>> >
>>> > I've run the main logic through Lua on the terminal and it works:
>>> >
>>> > $ lua
>>> > Lua 5.3.3  Copyright (C) 1994-2016 Lua.org, PUC-Rio
>>> >> comment = "<!-- blah -->"
>>> >> comment = comment:gsub("%<%!%-%- blah %-%-%>", "## blah")
>>> >> print (comment)
>>> > ## blah
>>> >
>>> > But I'm failing to integrate it with Pandoc (no change is registered in
>>> > file.html). It's probably due to my misunderstanding of functions (not
>>> a
>>> > programmer!).
>>> >
>>> > TIA.
>>> >
>>> > /pm
>>> >
>>> > --
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>>> .
>>>
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