PHP DOMNode append after comment

Question

Good Day,

I need help with little fringe case application of PHP and DOM manipulation/ordering. Basically I need help with a proper "appendAfter" function as to my knowledge PHP DOMNode only has "appendBefore".

I have an XML file like below, that I am using a PHP web interface to add/remove elements from.

<shelf>
    <shelf-id>1</shelf-id>
    <somerandomthings>xyz</somerandomthings>
    <!-- AAAAAAAAAAAAAAAAAAAA -->
    <book>
        <book-name>Alphabets</book-name>
        <book-color>Rainbow</book-color>
    </book>
    <book>
        <book-name>Animals</book-name>
        <book-color>Orange</book-color>
    </book>    
    <!-- BBBBBBBBBBBBBBBBBBBB -->
    <book>
        <book-name>Boats</book-name>
        <book-color>Green</book-color>
    </book>
    <!-- CCCCCCCCCCCCCCCCCCCC -->
    <book>
        <book-name>Cars</book-name>
        <book-color>Red</book-color>
    </book>    
    <!-- DDDDDDDDDDDDDDDDDDDD -->
    <!-- EEEEEEEEEEEEEEEEEEEE -->
    <!-- ETC...ETC...ETC..ETC -->
    <!-- PPPPPPPPPPPPPPPPPPPP -->
    <book>
        <book-name>Planes</book-name>
        <book-color>Blue</book-color>
    </book>
    <book>
        <book-name>Planets</book-name>
        <book-color>Silver</book-color>
    </book>
    <!-- TTTTTTTTTTTTTTTTTTTT -->
    <book>
        <book-name>Trees</book-name>
        <book-color>Brown</book-color>
    </book>
    <!-- RRRRRRRRRRRRRRRRRRRR -->
    <book>
        <book-name>Reptiles</book-name>
        <book-color>Green</book-color>
    </book>
    <!-- ZZZZZZZZZZZZZZZZZZZZ -->

    <somemorerandomthings>xyz</somemorerandomthings>
</shelf>

Since this file has a strict list of "allowed" tags I decided to use comments to mark out the various sections. (to feed my OCD of-course) i.e.

<!-- AAAAAAAAAAAAAAAAAAA -->

would mark the spot where all book-names starting with "A" are placed in alphabetical order.

I create a new book element like:

<book>
    <book-name>Zoos</book-name>
    <book-color>Grey</book-color>
</book>

So, what I decided to do was just append the new book to the main shelf element (this places it last (i.e. below "<somemorerandomthings>" element) I then select all the "book" elements, sort them and loop thorough all the comment tags, adding them at the appropriate position.

$commentmarker_path = "//shelf/comment()";

foreach (range('B', 'Z') as $alphabet) {
    $comment_id = str_repeat ($alphabet,20);
    $commentmarker = $xpath->query($commentmarker_path."[contains(.,'$comment_id')]"); 
    foreach( $sorted_books as $book_s ) 
        {
        $shelf_elm->item(0)->insertBefore($book_s, $commentmarker->item(0));
        }    
}

My loop selects the "B" marker and inserts all the "A" books before here. then the "C" marker and inserts all "B" books before it. etc...

The issue is with books starting with "Z". I would have liked to be able to add/sort all books in my main loop above. Currently I have code outside to select the somemorerandomthings element and then add the "Z" books. This could pose an issue if someone moves that element.

Side note, I tried running the loop from "A" -> "Z" and using the $commentmarker->item(0)->nextSibling as the marker point at which to insert. However because I am "inserting" into the original DOM element, the "A" markers next sibling is the Alphabets Book element and not the "B" marker.

Apologies for the lengthy question, hope it is understandable.

Thanks.