Find next heading

It can be very convenient to specify something like slide titles using headings as they have a dedicated Typst syntax. While it might suffice to just style how a heading is displayed using a show rule, this is not feasible when the slide title is supposed to be part of the page header, for example.

For these situations, the toolbox provides #toolbox.next-heading. It takes a function mapping the body of the first heading on the same page (if it exists) to some content.

The intended use is as such:

#set page(
  paper: "presentation-16-9",
  header: toolbox.next-heading(h => underline(h))
)

#show heading.where(level: 1): none

#set align(horizon)

#slide[
  = My slide title

  #lorem(10)
]

#slide[
  slide without a title
]

#slide[
  = Another title

  #lorem(10)
]

Note the extra show rule for level-one headings making them invisible.

You can make #toolbox.next-heading look for headings of other levels as well, just specify the optional level argument that defaults to 1.