It doesn't appear to be parsing at all. It's just looking for patterns.

If you look at languages.json in RulesEngine/Resources, files with the extension .html (and some others) are recognized as "html", with type "code":

  {
    "name": "html",
    "extensions": [ ".html", ".htm", ".cshtml", ".tmpl" ],
    "type": "code"
  },

This sets the scope for the patterns in AppInspector/rules/default; e.g.,

  {
    "name": "Content Management Framework: Wordpress",
    "id": "AI021200",
    "description": "Development Framework: Wordpress",
    "applies_to": [ "javascript", "html" ],
    "tags": [ "Framework.CMS.Wordpress" ],
    "severity": "moderate",
    "patterns": [
      {
        "pattern": "wordpress",
        "type": "string",
        "scopes": [ "code", "comment" ],
        "modifiers": [ "i" ],
        "confidence": "high"
      }
    ]
  },

This seems like it would be prone to a lot of false positives, but I haven't tried the tool.