The class on each page's wrapper, carrying data-page and the hidden attribute.
Remarks
Both pages stay MOUNTED once visited (see InsertFunctionWizard), so "is this page up" is a
question about hidden, not about what is in the document: .insert-function-page[data-page="…"]:not([hidden]).
The class on each page's wrapper, carrying
data-pageand thehiddenattribute.