I was using your first code which has $id->text instead of $id->content. Using "content" made the trick.

I am using the first script because of the nice loop. My final goal is to wrap the matching string(s) between tags (a simple replacement of match with tag+match+tag should do it). The hard part is that I need to match n-grams that possibly are split between two nodes (end of 1st node and begin of next one), with the loop I may find some working solution (my idea is to scan a window of two nodes at a time). Why this? Because I am parsing the output of pdftohtml which splits natural language sentences into lines, each line wrapped in its own tags. In the example above, it could be that I need to match the 2-gram "Translation is", which is in 2 adjacent DOMs. This is quite challenging (at least for my 0-parsing-abilities), but you have brought me near my goal. So time to play now.

Edit

Just for the sake of experimenting/learning, I tried with these two HTML snippets:

my $html = '<ul><div class="txt" style="position:absolute; left:84px; 
+top:73px;"><span id="f1" style="font-size:11px;vertical-align:baselin
+e;color:rgba(0,0,0,1);">technology of S2S translation, <b>also</b> kn
+own as Spoken Language Translation (SLT),</span></div><div class="txt
+" style="position:absolute; left:44px; top:73px;"><span id="f1" style
+="font-size:11px;vertical-align:baseline;color:rgba(0,0,0,1);">is a n
+ew application of AI,</span></div><li>there</li><li>everyone</li></ul
+>
';

my $html = '<ul><div class="txt" style="position:absolute; left:84px; 
+top:73px;"><span id="f1" style="font-size:11px;vertical-align:baselin
+e;color:rgba(0,0,0,1);">technology of S2S translation, <b>also</b> kn
+own as <p>Spoken</p> Language Translation (SLT),</span></div><div cla
+ss="txt" style="position:absolute; left:44px; top:73px;"><span id="f1
+" style="font-size:11px;vertical-align:baseline;color:rgba(0,0,0,1);"
+>is a new application of AI,</span></div><li>there</li><li>everyone</
+li></ul>
';
[download]

With the first HTML, using your first script with $id->text, <b>also</b> is not shown, with the second yes. I do not see any rational behind it...