support for HTML blocks that stay untouched

lib/markdown.js

@@ -719,7 +719,22 @@ Markdown.dialects.Gruber = {
 
     para: function para( block, next ) {
       // everything's a para!
-      return [ ["para"].concat( this.processInline( block ) ) ];
+
+      // For any markup that is not covered by Markdown’s syntax, you simply use HTML itself.
+      // There’s no need to preface it or delimit it to indicate that you’re switching from Markdown to HTML; you just use the tags.
+      // The only restrictions are that block-level HTML elements — e.g. <div>, <table>, <pre>, <p>, etc. — must be separated from
+      // surrounding content by blank lines, and the start and end tags of the block should not be indented with tabs or spaces.
+      // Markdown is smart enough not to add extra (unwanted) <p> tags around HTML block-level tags.
+      if (block[0] == "<" && block[block.length-1] == ">") {
+          var blockStr = block.valueOf();
+          // Span-level HTML tags — e.g. <span>, <cite>, or <del> — can be used anywhere in a Markdown paragraph, list item, or header. 
+          if (/^<(span|cite|del)[\s>]/.test(blockStr)) {
+              return [ ["para"].concat( this.processInline( block ) ) ];
+          }
+          return [ ["html"].concat( blockStr ) ];
+      } else {
+          return [ ["para"].concat( this.processInline( block ) ) ];
+      }
     }
   }
 }
@@ -1297,6 +1312,11 @@ function render_tree( jsonml ) {
       attributes = {},
       content = [];
 
+  // render block as-is
+  if (tag === false) {
+      return jsonml.join( "" );
+  }
+
   if ( jsonml.length && typeof jsonml[ 0 ] === "object" && !( jsonml[ 0 ] instanceof Array ) ) {
     attributes = jsonml.shift();
   }
@@ -1367,6 +1387,10 @@ function convert_tree_to_html( tree, references, options ) {
     case "para":
       jsonml[ 0 ] = "p";
       break;
+    case "html":
+      // handle block as-is
+      jsonml[ 0 ] = false;
+      break;
     case "markdown":
       jsonml[ 0 ] = "html";
       if ( attrs ) delete attrs.references;