Diagnose Slidify Error

diagnose_error.R

library(markdown)
re.capture <- function(pattern, string, ...) {
  rex = list(src = string, names  = list(),
    result = regexpr(pattern, string, perl = TRUE, ...))
  
  for (.name in attr(rex$result, 'capture.name')) {
    rex$names[[.name]] = substr(rex$src, 
      attr(rex$result, 'capture.start')[,.name], 
      attr(rex$result, 'capture.start')[,.name]
      + attr(rex$result, 'capture.length')[,.name]
      - 1)
   }
  return(rex)
}

raw_md <- "\n### Slide 1 ###\n\nThis is an unordered list \n\n- Point 1\n- Point 2\n- Point 3\n- Point 4"
content <- renderMarkdown(text = raw_md, renderer.options = markdownExtensions())
hpat <- '(?<header><h(?<level>[0-9])>(?<title>.*)</h[0-9]>)\n+'
vars <- re.capture(hpat, content)$name
print(vars)