title: Span tag and content not rendering inside quill editor
body: <p>I have recently started exploring quill to implement a rich text editor. I want to render following html content in quill editor:
  Second span</p>
  
  <p>However when rendered, span tag is removed and its content is wrapped inside P tag and rendered. I learnt that as part of optimization quill removed span tags. But I really want span tag to render so I added a SPAN blot extending BlockEmbed. However after adding SPAN blot, nothing rendered in the editor. I don't understand what I am doing wrong; Here is the SPAN Blot:</p>
  
  <pre><code>let quill = require("quill");
  let BlockEmbed = quill.import("blots/block/embed");
  
  class SpanBlot extends BlockEmbed {
      public static create(value: any): any {
          let node = super.create(value);
          node.setAttribute("data-embed-id", value);
          return node;
      } 
  
      public static value(node: any): any {
          return node;
      }
  
      public static formats(node: any): any {
          let format: any = {};
          if (node.hasAttribute("data-embed-id")) {
              format.height = node.getAttribute("data-embed-id");
          }
          return format;
      }
  
      public formats(): any {
          let formats = super.formats();
          formats["span"] = SpanBlot.formats(this.domNode);
          return formats;
      }
   }
  
  SpanBlot.blotName = "Span";
  SpanBlot.tagName = "SPAN";
  SpanBlot.class = "social";
  
  export { BlockEmbed, SpanBlot };
  </code></pre>