Cloning template content preserves the reusable blueprint

Appending original template content consumes its fragment, so repeated instances should receive independent copies instead.

A reusable blueprint must survive insertion; otherwise, later components inherit an empty structure rather than their intended interface.

MDN documents that insertion moves fragment children into the destination, leaving the original fragment empty.

Importing content into the target document also makes the intended custom element registry available during cloning.

Because DOM exposes mutable nodes, template composition requires deliberate ownership of each instance.

Attach programmatic listeners to copied elements, and avoid duplicate identifiers when inserting copies into the same document.

Preserve the source fragment as a blueprint, then customize each copy before inserting it into its destination.