You're supposed to only use custom elements with a dash in the name. Otherwise the spec can add an element that means something new, and you've accidentally used that name.

For that to work I would need to define a custom component from JavaScript, wouldn't I? (and I thought custom components had to contain an hyphen in there name, is that wrong?)

try it!

  data:text/html,<grid><p>A</p><p>B</p><p>C</p></grid><style>grid{display: grid}</style>

afaik to create a CustomElement you need to use dashes, yes, but in this example `<grid>` is an HTMLUnknownElement, which renders just fine. some discussion here: https://stackoverflow.com/a/22545622/2393963

TIL thx!