Text Formats and Allowed HTML

Anchors are attributes on <a> elements, so they only survive a save if the text format permits those attributes. This page explains what has to be allowed and how the module interacts with core's HTML filtering.

The attributes involved

Attribute	Purpose
`id`	The anchor itself. This is the jump target.
`name`	Legacy form of the same thing, still read for backwards compatibility.

Limit allowed HTML tags

When a format enables the Limit allowed HTML tags and correct faulty HTML filter, only the listed tags and attributes survive. The anchor plugin declares what it needs, and Drupal merges those into the allowed HTML when you save the format.

A format with the Anchor button typically ends up with something like:

<a href hreflang id name>

You normally do not edit this by hand. Two cases where you might:

The format was configured before the Anchor button was added and the merge did not run, for example because the configuration was imported rather than saved through the form.
The allowed HTML is managed in exported configuration and you want it explicit.

To check, edit the format and read the Allowed HTML tags field. If id is absent from the <a> entry, anchors will be stripped on save.

The `name` attribute and the post update

Support for the legacy name attribute was added after some sites had already been using the plugin. Those formats' allowed HTML predates it, so the module ships a post update:

anchor_link_post_update_allow_anchor_name_attribute

It finds every text editor that has the anchor plugin enabled, and for each one whose format uses filter_html, appends <a name> to the allowed HTML.

Run it as part of a normal update:

drush updatedb

The post update only touches formats that already have the plugin enabled. It does not enable anything, and it does not widen formats that never used anchors.

Configuration management note

Because the post update edits filter.format.* configuration, running it changes active configuration. On a site that manages configuration in code, run drush updatedb and then export:

drush updatedb -y
drush config:export

Otherwise the next config:import reverts the change and anchors start being stripped again.

General HTML Support

Drupal core's Arbitrary HTML support plugin (General HTML Support in CKEditor terms) can also claim <a> attributes, which conflicts with the anchor plugin.

The module resolves this by altering that plugin's definition to disallow it from handling the attributes the anchor plugin owns:

a with attributes id and name

This happens in hook_ckeditor5_plugin_info_alter(). The practical effect is that a format with Full HTML style arbitrary HTML support and the Anchor button both enabled behaves correctly, with the anchor plugin in charge of anchors.

You do not need to configure this, but it is worth knowing if you are debugging attribute loss on a Full HTML format.

Editor class versus saved markup

The ck-anchor class is an editor concern. It marks anchors so CKEditor can show the "INVISIBLE ANCHOR" flag and let authors select empty anchors.

It is not written to the saved content. If you see class="ck-anchor" in your rendered HTML, the editor library is out of date. Update to vardot/ckeditor5-anchor-drupal 2.0.5 or newer.

Troubleshooting

Anchors disappear on save. id is not in the allowed HTML for <a>. Re-save the text format through the form so the merge runs, or add it explicitly.

Anchors work on Full HTML but not on a restricted format. Same cause. Full HTML does not filter, so it hides the problem.

ck-anchor appears in rendered output. Editor library too old. Check libraries/ckeditor5-anchor-drupal/package.json for the installed version.

Legacy name anchors stopped working after an upgrade. The post update has not run, or ran and was then reverted by a configuration import. See the note above.