Need help with creating text anchors with tagged text.

Read, I'm not sure the following is going to help you. It works for external hyperlinks, but you want internal links, right? Anyway, it might give you some clues.

A funny thing: I was reviewing some script where I got links to work, and I spotted a tiny coding error. Links seemed to be defined by two separate identifiers: a "link name", which is what appears in Edit Hyperlink dialog, and a "Dest Key", which seems to be a simple increasing number. However, due to aformentioned coding error, the dest keys between the actual link and its definition were off by '1', so there was no way that ought to have matched. But it still worked! So "Dest Key" is a red herring ...

As far as I understand, it works like this (for hyperlinks): in your text, you have

1. HplName -- this is actually the 'title' that appears in the Hyperlink palette
2. HplDest -- this is the 'internal name'
3. DestKey. Hm. Perhaps you could omit this, per above obsvn.
4. CharStyleRef, the name of the auto-applied style
5. Hid -- seems to be always '0'
6. HplOff: the "offset" from this entire command to the start of the hyperlink, in InDesign characters.
7. HplLen: the "length" from the hyperlinked text, in InDesign characters.

and in the list of 'proper' definitions, those that appear at the very end of your file:

1. HplDestDfn -- the internal name again
2. DestKey -- see above
3. HplDestUrl -- finally! A real URL! (But you must escape lots of characters, such as the forward slash and colon.)
4. Hid -- again, always seems to be '0'.

Some of these items are perhaps optional, but experimenting with what may be left out only lead to frustration The Tagged Text guide is far from complete, as I'm sure you already knew.

As noted, some (or all) of the named items need a backslash escape for a few characters, but I can't find a definitive way to determine in advance what is 'good' and what is 'not good'.

The following script creates a Tagged Text file with a couple of working hyperlinks in it -- I don't know if this is of any help for your internal links.

var hyperlinkDest = [];
var text = "This is some text with a link [http://www.jongware.com/idjshelp.html] and another one [http://forums.adobe.com/thread/1014617?tstart=0] in it.";
var tagtext = text.replace (/\[(.+?)\]/g, function (full, match)
          {
                    return makelink (match, 'title:'+match, match, match);
          }
);
// When done processing plain text, add the destinations at the end:
tagtext += hyperlinkDest.join('');
tagFile = File(Folder.myDocuments+'/__tmp.txt');
if (tagFile.open('w') == false)
{
          alert ("Unable to create temporary file!");
          exit();
}
if (File.fs == "Windows")
          tagFile.write ("<ASCII-WIN>\n");
else
          tagFile.write ("<ASCII-MAC>\n");
tagFile.write ("<dcs:HYPERLINK=<cu:1>>\n");
          tagFile.write (tagtext);
tagFile.close();
   
// 'text' is the actual text that will be clickable
// 'title' is what will appear in the Hyperlinks palette
// 'name' is the internal name in the Edit Hyperlink dialog
// 'url' is the actual URL that will be linked to
function makelink (text, title, name, url)
{
          var destkey = hyperlinkDest.length;
          // In URL you must escape forward slashes and colons
          // .. and some other characters as well, by the way. There seems to be no list 
          url = url.replace(/\//g, '\\/').replace(/:/g, '\\:');
          hyperlinkDest.push ('<HplDestDfn:=<HplDestName:'+name+'><DestKey:'+String(destkey)+'><HplDestUrl:'+url+'><Hid:0>>');
          return '<Hpl:=<HplName:'+title+'><HplDest:'+name+'><DestKey:'+String(destkey)+'><CharStyleRef:HYPERLINK><Hid:0><Brdrv:0><HplOff:0><HplLen:'+String(text.length)+'>>'+text;
}