hasClosingTag = (match, { after }) => {
        const tag = "</" + match[0].slice(1);
        const pos = match.input.indexOf(tag, after);
        return pos !== -1;
      }
Takes a string like "<Booger" and checks to see
if we can find a matching "</Booger" later in the
content.
@param {RegExpMatchArray} match
@param {{after:number}} param1