APL with the fiirst letter (automatically). Do you know how?

Rick, the core is this:

KLD_Z.InsertGroupTitles = function (oDoc, sExcludes) { // ==================
/*            Insert group title character in (alphabetic) lists similar to indexes
Arguments     oDoc            Current document
              sExcludes       List of characters which can be the first in a paragraph, but shall be skipped.
                              An example are start apostrophes «‹“„
Returns       true for success, false in case of an error
Calling       ExecuteFCodes, GetTheText, Message
Comment       • The process starts with the paragraph of the current location.
              • Any change of the first character (Or second, in case the first is an exlude)
                triggers the insertion of a paragraph with format GroupTitlesIX.
                If this is not in the catalogue, it will be created.
              • The process halts either at the end of the document or if a paragraph starts
                with the special character "optional hypehn", x04
History       2022-03-22
*/
var msg_01, CRLF="\x0A" , oPgf, oPgfID, oPgfFmt, oPgfProps, oTL1, oTL2, oTR,
    sBegin = "\xFF", sChar, sFirst, sParaFormat = "GroupTitlesIX", sTermination = "\x04";
  msg_01 ="Current location is not in a paragraph."
  msg_02 ="Paragraph format for the group titles (GroupTitlesIX) is not in catalgoue → it has been created.\nYou will need to define the format (font, size etc.) properly."

function GetFirst2Chars (oDoc, oPgf, sExcludes) {
var oTL1 = new TextLoc(), oTL2 = new TextLoc(), oTR, sChar, sFirst;
  oTL1.obj = oTL2.obj = oPgf;
  oTL1.offset = 0;
  oTL2.offset = 2;
  oTR = new TextRange (oTL1, oTL2)
  sFirst = KLD_Z.GetTheText(oDoc, oTR);           // first 2 chars
  sChar = sFirst.substr (0, 1);
  if (sExcludes.indexOf (sChar) < 0) {
    sFirst = sChar;
  } else {
    sFirst = sFirst.substr (1, 1);                // skip excluded char
  }
  return sFirst;
} // --- End of GetFirst2Chars -------------------

  oPgf = oDoc.TextSelection.beg.obj;
  if (!oPgf.ObjectValid()) {
    KLD_Z.Message ("E", msg_01, "InsertGroupTitles");
    return false;
  }
  oPgfFmt = oDoc.GetNamedObject(Constants.FO_PgfFmt, sParaFormat);
  if (!oPgfFmt.ObjectValid()) {
    oPgfFmt = oDoc.GetNamedObject(Constants.FO_PgfFmt, "Body");
    oPgfProps = oPgf.GetProps();
    oPgfFmt = oDoc.NewNamedObject (Constants.FO_PgfFmt, sParaFormat); // define new ¶ format
    oPgfFmt.SetProps(oPgfProps);
    KLD_Z.Message ("I", msg_02, "InsertGroupTitles");
  }
  sFirst = GetFirst2Chars (oDoc, oPgf, sExcludes);// --- Get first char in this paragraph not excluded

  while (sFirst != sTermination) {
    if (sBegin != sFirst) {                       // ---  insert pargraph with grouptitle
      oTL1 = new TextLoc (oPgf, 0);
      oDoc.AddText (oTL1, sFirst + CRLF);         // insert title line
      KLD_Z.ExecuteFCodes(["IPToPrevParaStart"]); // go back to inserted line
      oPgfProps = oPgfFmt.GetProps();
      oPgf.SetProps(oPgfProps);                   // apply ¶ format
      KLD_Z.ExecuteFCodes(["IPToNextParaStart"]); // skip the insertion
    }
    sBegin = sFirst;                              // --- sBegin is the new first character
    oPgf = oPgf.NextPgfInFlow;                    // --- Take next paragraph
    if (!oPgf.ObjectValid()) { break;}            // end of document
    sFirst = GetFirst2Chars (oDoc, oPgf, sExcludes);
  }
  return true;
} // --- end InsertGroupTitles ---------------------------------------------------