I would have thought a perfect use case for #QuartoPub "includes" would be something like:

#| label: conditional-include
if ( condition1) {
  {{< include _condition1.qmd >}}
} else {
  {{< include _condition2.qmd >}}
}

But {quarto} complains about incomplete input if I actually do that. But both docs look fine.

Guess it's figuring out the whole document pieces to include outside first, cat together, and then render.

#RStats