<iframe> and some HTML tags are not show in wysihtml5 editor

Question

I want to use iframe code in wysihtml5 editor. I have used

$('.script_texteditor').wysihtml5({

and

$(function () {
$('.script_texteditor').wysihtml5({
      "stylesheets": ["css/wysiwyg-color.css"], // CSS stylesheets to load
      "color": true, // enable text color selection
      "size": 'small', // buttons size
      "html": true, // enable button to edit HTML
      "format-code" : true, // enable syntax highlighting
      "font-styles": true, //Font styling, e.g. h1, h2, etc. Default true
      "link": true, //Button to insert a link. Default true
      "font-type": true, 
      "image":true, //Button to insert an image. Default true,
      "fontFamilySelection": true,
      "emphasis": true, //Font styling, e.g. h1, h2, etc. Default true
      "lists": true, //(Un)ordered lists, e.g. Bullets, Numbers. Default true
      "blockquote": true, //Blockquote  
      "iframe": {
            "check_attributes": {
                "src": "url"
            }
       }    
    });
});

I have used this javascript code in textarea tag:

<TEXTAREA class="form-control script_texteditor" NAME=script_text ROWS=20 COLS=50></TEXTAREA>

My question is why some html tags and iframe tag not enable?