Add explanation on conditional code execution

docs/authoring/conditional.qmd

@@ -25,6 +25,16 @@ You can also set conditions on non-executable code blocks:
 ```
 ````
 
+When using the `knitr` engine, if you want to have a code chunk being excecuted/evaluated only when the output is being rendered to HTML or LaTeX you can use the `is_html_output()` and `is_latex_output()` respectively (see [this reply to quarto-cli issue 11724](https://github.com/quarto-dev/quarto-cli/issues/11724#issuecomment-2557635192)).
+
+```` markdown
+``` {r .content-visible when-format="html"}
+#| eval = !expr knitr::is_html_output()
+# code is shown AND evaluated only in HTML
+2+2
+```
+````
+
 To apply a condition only to a part of a paragraph, use a span (`[]{}`):
 
 ``` markdown