[Martin Ferret (MartinFerret)]

Fixes microsoft/TypeScript#63556

document.createElementNS("http://www.w3.org/1999/xhtml", "div") currently returns HTMLElement, while the SVG and MathML namespaces already have a generic overload that maps the tag name to the right element type.

This adds the matching overload for the XHTML namespace, placed before the existing string overload (same pattern as SVG and MathML):

createElementNS<K extends keyof HTMLElementTagNameMap>(namespaceURI: "http://www.w3.org/1999/xhtml", qualifiedName: K): HTMLElementTagNameMap[K];

• Known tag names now return the specific type ("div" -> HTMLDivElement).
• Unknown tag names and string values still return HTMLElement.
• A unit test is added in unittests/files/createelementns.ts.

Note: like createElement, a variable declared with let el = document.createElementNS(xhtml, "div") is now typed HTMLDivElement, so assigning a different element type to it later becomes an error.

[github-actions]

Thanks for the PR!

This section of the codebase is owned by Kagami Sascha Rosylight (@saschanaz) - if they write a comment saying "LGTM" then it will be merged.

[Kagami Sascha Rosylight (saschanaz)]

Looks good, thanks! LGTM

[github-actions]

Merging because Kagami Sascha Rosylight (@saschanaz) is a code-owner of all the changes - thanks!