One DOM id per element, and the references inside a snippet follow when one has to change.

Why a second copy is not the same document twice

Everything the palette offers is a worked EXAMPLE, and an example names things: the kit's delete dialog ships id="modal-delete-page" with id="btn-delete-cancel" beside it, and its newsletter dialog ships an <input id="modal-newsletter-email"> with a <label for="modal-newsletter-email"> pointing at it. Those names are most of what makes an example readable. Placing one twice — which is the ordinary way to build a second dialog — put two elements in the document answering to one id, and a duplicate id is not a cosmetic fault:

• JS.exec("data-pb-open", to: "#modal-delete-page") reaches whichever came first, so the author's second button opens the first dialog
• document.getElementById and every phx-target behave the same way
• LiveView refuses to patch a container it cannot tell apart and raises

The arrival yields

arrived is the node ids the op just created, and they are the ones renamed — the same rule, and for the same reason, that MishkaCmsCore.Runtime.PageBuilder.PageForms.Naming.dedupe/2 follows. Renaming in document order would rewrite the dialog already on the page whenever the new one was dropped above it, and that dialog is the one whose id an author has already written a handler, a link or an interaction against.

Numbering fills gaps rather than counting: modal-delete-page beside modal-delete-page-3 mints modal-delete-page-2, so deleting the second of three copies does not push the next to -4.

References move with the name

Renaming the copy's dialog and leaving the copy's button pointing at the original would be worse than the collision — the author would have two buttons that both open the first dialog and no visible reason why. So every reference to the old id is rewritten, in three shapes, and only WITHIN the nodes that arrived:

• a selector anywhere in a value, string or expression — to: "#modal-delete-page", href, data-cancel
• a quoted literal inside an expression — show_modal("modal-delete-page")
• a bare id in an attribute that takes one — for, aria-controls, headers and friends, including the space-separated lists three of them accept

Nodes that were already on the page are never touched: they point at the original id, the original still has it, and they are right.