title: Can I use YAML data from a child .Rmd as first level heading for a pagedown document?
body: <p>I would like to use child rmarkdown documents as "chapters" in my pagedown document and have the YAML options from that child document, such as <code>title:</code>, be used as a first level section heading. Ideally all section headings in the child .Rmd would then be changed to one level lower.</p>
  
  <p>I did my best to go through the extensive and wonderful documentation of bookdown and pagedown and rmarkdown but haven't been able to figure out how to accomplish this.</p>
  
  <p><strong>Parent Rmd</strong>:</p>
  
  <pre><code>---
  title: Parent Title
  output: pagedown::html_paged
  ---
  
  # Parent First level header
  
  Some text.
  
  ```{r, child='child.Rmd'}
  
  </code></pre>
  
  <p><strong>Child Rmd</strong>:</p>
  
  <pre><code>---
  title: Child Title
  ---
  
  # Introduction
  
  Some child text.
  
  </code></pre>
  
  <p><strong>Desired Result</strong>:</p>
  
  <pre><code>---
  title: Parent Title
  output: pagedown::html_paged
  ---
  
  # Parent First level header
  
  Some text.
  
  # Child Title
  
  ## Introduction
  
  Some Child text.
  
  </code></pre>