Example of .Rmd, with YAML trying to interpret code and objects set later in document

example.Rmd

---
title: 'How do I interpret R code in YAML?'
author: Jeff Hollister
output:
  pdf_document:
    fig_caption: yes
    keep_tex: yes
    number_sections: yes
  html_document: null
  word_document: null
fontsize: 11pt
capsize: normalsize
csl: components/ecology.csl
documentclass: article
abstract:  This is a test.  Is this `r mean(x)` working?
---

This is a test of outputing a pdf, with R code interpretted in the YAML front mater.  Use case for this would be a manuscript, with abstract as part of YAML, and some of the results in the abstract being calculated in the body of the Rmd.  For instance:

```{r}
x<-rnorm(100)
mn<-mean(x)
mn
```