Please note that CKEditor 4 reached its End of Life (EOL) in June 2023. From then on, it receives no more updates, new features, bug fixes, and most importantly, security patches.
If you have an active CKEditor 4 subscription and need help, you can contact our support team. If you are not ready to migrate yet, for a limited time we are offering a paid Extended Support Model that will protect you against security vulnerabilities and/or breaking third-party API changes.
CKEditor 4 is a standards-compliant (W3C) HTML editor which means it corrects code if it doesn’t follow current web standards. What’s more, some browsers may have their own interpretation of HTML.
Also, CKEditor 4 is featured with Advanced Content Filter (ACF) which transforms and removes disallowed elements. If you paste content into CKEditor 4 and notice that some elements are removed, then chances are high that it was removed by ACF. For instance, if your toolbar doesn’t include the Bold button, CKEditor 4 will strip bold tags from the source code.
See an online demo of how ACF works in CKEditor 4 Examples.