How can I hide everything before the last occurrence of a label?

Questions
2

This is a bit tricky… I don’t think a query can do it. For the case you showed, the following works:

#let last-position(arr, searcher) = {
  let rev-index = arr.rev().position(searcher)
  if rev-index != none {
    arr.len() - rev-index - 1
  }
}

#show: body => {
  let index = last-position(body.children, item => item.fields().at("label", default: none) == <thelabel>)
  body.children.slice(index).join()
}

#metadata("something") <thelabel>

A

#metadata("something") <thelabel>

B

However this depends on inspecting content, and that can be hard to do right. if the label is instead nested in, say, an emphasis element, my solution won’t find it:

#metadata("something") <thelabel>
// ^ now this is the last match!

A

_#metadata("something") <thelabel>_

B

What’s the end goal you’re after? Maybe there’s a different way to achieve it?