Checking if content is html

XWikiDocument.display:

if (isInRenderingEngine && !is10Syntax(syntaxId)
  && (result.indexOf("<") != -1 || result.indexOf(">") != -1)) {
    result.insert(0, "{{html clean=\"false\" wiki=\"false\"}}");
    result.append("{{/html}}");
}

Add check for '&', e.g. to handle  

I would need such a function in another place too, so maybe it could be defined as utility function, such as HtmlUtil.isHtml(StringBuffer) + HtmlUtil.isHtml(String)

Or perhaps HtmlUtil.isNotHtml would be more appriopriate... because if string doesn't contain any of <>& then it is not html, but if it does it not necessarily is (e.g. "M&M")