Roundcube + how to display arbitrary code?

Question

PHP

Hi all.
Such a task is worth it.
Display a specific list of contacts from the database when creating a letter and put this list as a select in the to whom field.
In the PHP code in the compose.inc file, I deduced the list I needed. But I can't display it in HTML code.
Since roundcube works with tags that I don't understand.

<tr>
    <td class="title top"><label for="_to"><roundcube:label name="to" /></label></td>
    <td class="editfield">
      <roundcube:object name="composeHeaders" part="to" form="form" id="_to" cols="70" rows="1" tabindex="2" />
    </td>
  </tr>

this is the input field of the recipient's address where I want to display the select