getElementsByTagNameHierarchy

Requirements

• Export getElementsByTagNameHierarchy(root, tags) as named and default. root is an Element, Document, or DocumentFragment; tags is a readonly array ordered from ancestor to final descendant. Return matching final elements in depth-first document order.
• The hierarchy uses direct parent-child links, not arbitrary descendant gaps. Its first tag may start anywhere strictly below root. Root itself is excluded from both results and matching chains. A single tag behaves like getElementsByTagName.
• Match HTML tags case-insensitively; * matches any element at that position. Repeated tags and overlapping chains are allowed, but return each matching element only once. Empty tags returns an empty array.
• Every tag must be * or match /^[a-z][a-z0-9-]*$/i. Reject non-array hierarchies and invalid entries with TypeError before traversal. Namespace-specific matching is excluded.
• Use your own traversal; do not call querySelector, querySelectorAll, native getElementsByTagName, TreeWalker, or NodeIterator. Ignore text/comments and do not mutate the DOM or tags. Support detached roots and fragments; return a snapshot array.

Examples

Input: getElementsByTagNameHierarchy(root, ["section","div","button"])
Output: Buttons with a direct div parent and section grandparent, all strictly below root.

Input: getElementsByTagNameHierarchy(root, ["*","BUTTON"])
Output: Buttons with an element parent below root.