Why is CKEditor refusing my custom tag? - plugins

Question

With a custom CKEditor plugin I am trying to insert a custom HTML tag, but the tag gets removed as soon as it is inserted into the editor. My plugin.js file:
CKEDITOR.plugins.add( 'tweet', {
icons: 'tweet',
init: function( editor ) {
editor.addCommand( 'insertTweet', {
allowedContent: 'tweet[:id]',
requiredContent: 'tweet',
exec: function( editor ) {
console.log('inserting');
editor.insertHtml( '<tweet :id="\'123\'" />' ); // also tried <tweet />
// editor.insertHtml( '[tweet :id="\'123\'" /]' ); // this works
}
});
editor.ui.addButton( 'tweet', {
label: 'Insert tweet',
command: 'insertTweet',
toolbar: 'insert,0'
});
}
});
The way I am adding the plugin for Bolt CMS backend:
function run() {
var extrasAdded = false;
if (typeof(CKEDITOR) == 'undefined') return;
CKEDITOR.plugins.addExternal('tweet', '/assets/plugins/tweet/plugin.js', '');
CKEDITOR.on('instanceReady', function (event, instance) {
if (extrasAdded === true) return;
var config = event.editor.config;
config.toolbar.push(
{ name: 'insert', items: [ 'tweet' ] }
);
config.extraPlugins += (config.extraPlugins ? ',' : '') + 'tweet';
config.extraAllowedContent = 'tweet'; // also tried 'tweet[:id]'
CKEDITOR.instances['body'].destroy();
CKEDITOR.replace('body', config);
extrasAdded = true;
});
}
if (document.readyState!='loading') run();
else document.addEventListener('DOMContentLoaded', run);
Can someone smart see why my tag is rejected?

Answer 1

So it turns out that we don't need the allowedContent or requiredContent properties in the plugin.js script. What did the trick was to tweak the editor's HTML DTD rules. In my case I got a reference to the editor in the instanceReady callback and tweeked it like this:
// name = 'tweet'
editor.filter.allow(name + "[!*]", name, true);
CKEDITOR.dtd[name] = CKEDITOR.dtd;
CKEDITOR.dtd.$empty[name] = 1; // allow self-closing tag
CKEDITOR.dtd.$blockLimit[name] = 1;
CKEDITOR.dtd.$nonEditable[name] = 1;
CKEDITOR.dtd.$object[name] = 1;
CKEDITOR.dtd.$inline[name] = 1; // $block won't work!
You can also see a full gist of it.