How to expose layout information as metadata?

[cAtte]

this is similar to how context produces opaque content blocks:

Why is the value I receive from context always content?

I am trying to use a counter to switch between displaying something and not displaying it. To do that, I check whether the counter is even and then increase it by one. #let my-counter = counter("my-counter") #let alternate(it) = { let value = context my-counter.get().first() if calc.even(value) { it } my-counter.step() } #alternate[I'm visible] #alternate[I'm not] #alternate[I'm again visible] However, when trying to use the value from the context, I get this error: error: expec…

in this case, what you wanna do is produce the labeled metadata from within the layout callback, which is where you actually have access to the value:

#layout(size => [#metadata(size.width.mm())<layout>])