[markdown mode] Allow HTML tags with dash and digits

mode/markdown/markdown.js

@@ -534,7 +534,7 @@ CodeMirror.defineMode("markdown", function(cmCfg, modeCfg) {
       return type + tokenTypes.linkEmail;
     }
 
-    if (modeCfg.xml && ch === '<' && stream.match(/^(!--|[a-z]+(?:\s+[a-z_:.\-]+(?:\s*=\s*[^>]+)?)*\s*>)/i, false)) {
+    if (modeCfg.xml && ch === '<' && stream.match(/^(!--|[a-z][a-z0-9-]*(?:\s+[a-z_:.\-]+(?:\s*=\s*[^>]+)?)*\s*>)/i, false)) {
       var end = stream.string.indexOf(">", stream.pos);
       if (end != -1) {
         var atts = stream.string.substring(stream.start, end);