This may not be exactly what you want but it is probabbly a little closer. I added the numbers after the tags to track which open/close pair I was looking at. Left 'em in. 
                                                                      
+                                                      
use strict;
use Parse::RecDescent;

my $parser = Parse::RecDescent->new(q(
                                    start: part(s)
                                          {
                                             print join("\n",@{$item[1
+]});
                                          }

                                      part : stag part(s) etag
                                             {
                                                 $return = "$item{stag
+} " . join(" ", @{$item[2]}) . " $item{etag}";
                                             }
                                             | stag data etag
                                             {
                                                 $return = "$item{stag
+} $item{data} $item{etag}";
                                             }
                                             | data



                                      data  : m{([^<]+)}

                                      stag : m{<open\d>}
                                      etag : m{<close\d>}
));

$parser->start(<DATA>);
__DATA__
<open1> Some content <close1> <open2> some <open3> more content <close
+3> <close2>

[download]
gives the following output 
<open1> Some content  <close1>
<open2> some  <open3> more content  <close3> <close2>

[download]
The formatting of the second clause can be twekaed with the join char.
I am by no means a P::RD master, but I really enjoy playing with it. Let me know if this helps.

In reply to Re: Parse::RecDescent and nesting by amw1
in thread Parse::RecDescent and nesting by b10m

Title:
Use:  <p> text here (a paragraph) </p>
and:  <code> code here </code>
to format your post, it's "PerlMonks-approved HTML":


  • Posts are HTML formatted. Put <p> </p> tags around your paragraphs. Put <code> </code> tags around your code and data!
  • Titles consisting of a single word are discouraged, and in most cases are disallowed outright.
  • Read Where should I post X? if you're not absolutely sure you're posting in the right place.
  • Please read these before you post! —
  • Posts may use any of the Perl Monks Approved HTML tags:
    a, abbr, b, big, blockquote, br, caption, center, col, colgroup, dd, del, details, div, dl, dt, em, font, h1, h2, h3, h4, h5, h6, hr, i, ins, li, ol, p, pre, readmore, small, span, spoiler, strike, strong, sub, summary, sup, table, tbody, td, tfoot, th, thead, tr, tt, u, ul, wbr
  • You may need to use entities for some characters, as follows. (Exception: Within code tags, you can put the characters literally.)
            For:     Use:
    & &amp;
    < &lt;
    > &gt;
    [ &#91;
    ] &#93;
  • Link using PerlMonks shortcuts! What shortcuts can I use for linking?
  • See Writeup Formatting Tips and other pages linked from there for more info.