How to use footnotes in custom fields

Hi @muhammadmairaj,

Thank you for your valuable feature request, that raised already much concern with this and at least one other plugin (EFN) alike.

Much like when footnotes are in the text of a widget or in the content of a popup, processing footnotes in the content of a custom field requires that when the custom field is displayed, certain filters be applied. Footnotes adds filters to the following hooks, per current version; to see them in the code:

https://plugins.trac.wordpress.org/browser/footnotes/tags/2.7.3/class/task.php#L434

From that code, the full list of filtered hooks, beside wp_head and wp_footer filtered for output only, is:

1. the_title
2. the_content
3. term_description
4. pum_popup_content
5. the_excerpt
6. widget_title
7. widget_text

From this I conclude that it depends on how a custom field is implemented. This is the code to apply one of these filters:

$the_custom_field_content = apply_filters( 
  'the_desired_hook_name', 
  $the_custom_field_content
);

Does that make sense? I hope that ACF does apply filters added to one of the cited hooks.

Out of curiosity, may I ask your which other footnotes plugin you consider using on failure of the Footnotes plugin to process footnotes in custom fields? As far as I know, other footnotes plugins may apply filters to less than the hooks listed above. E.g. the filter for pum_popup_content was added on request.

If we know the hook name that ACF applies the filters of, hopefully the Footnotes authors will add it likewise. Meanwhile, what I’m suggesting to do is applying the filters of one of the above hooks, conversely, when displaying the custom field. Sort of a quick fix.

Please let us know whether that solves the issue.

@muhammadmairaj,

No problem. Thank you for the insights. In wysiwyg fields, ACF applies the filters added to acf_the_content. Footnotes not working in plain text seems normal to me because of multiple Footnotes features requiring markup.

The references’ section displaying right after the field is often the expected behavior as in https://wordpress.org/support/topic/enhancement-request-8/ But you rightfully require that on the website you are running, footnotes be reunited at the bottom of the page. To achieve that, these custom fields would ideally be part of the content, and footnotes would be processed all at once when filters like the one added by Footnotes are applied to the_content.

Alternatively, custom fields might be appended to the post and add up to enhance the content if priority is higher than the one that the Footnotes filter is added with. This is controlled in the Footnotes settings under the third tab.

After all, given the trouble you are experiencing, I wonder whether custom fields are an optimal solution. Another option would be using tables instead. An already posted example with tables, footnotes, and all footnotes together at the bottom of the entry was a page of https://wikiwiki.in, but not all pages of the website do have footnotes.

Also you can go through ACF documentation to see what filters they use and alter your plugin’s coding accordingly.

ACF documentation is very extensive. In the plugin’s code (free version) we see the acf_the_content in the wysiwyg field content, in this file:

https://plugins.trac.wordpress.org/browser/advanced-custom-fields/tags/5.12/includes/fields/class-acf-field-wysiwyg.php#L43

I’m no more in a position to alter Footnotes’ code to provide quick fixes, but as it appears, that wouldn’t even be useful since fields must not be processed individually, per your requirement.

Please let us know if we can do anything else aiming at ACF-Footnotes-integration.