function wfTLDR(ast, file, setting) {
  const msgLevel = 'TL;DR headings must be level 3 or greater.';
  const msgHide = 'TL;DR headings must be hidden from the TOC with ' +
      ' `{: .hide-from-toc }`';
  visit(ast, 'heading', function(node) {
    let body = toString(node);
    if (reTLDR.test(body)) {
      if (node.depth < 3) {
        file.message(msgLevel, node);
      }
      if (!reHideFromTOC.test(body)) {
        file.message(msgHide, node);
      }
    }
  });
}
Remark Lint Test - verifies TL;DRs are at least L3 & hidden from the TOC.

@param {Object} ast
@param {Object} file
@param {Object} setting