This filter was added in Caldera Forms 1.4.5
When using the {summary} magic tag in Caldera Forms email notifications each field, and it’s value is displayed using a preset pattern. This pattern can be changed using the caldera_forms_summary_magic_pattern.
Please keep in mind that what you return on this filter must be a valid sprintf pattern. If not, form submission will probably break. This is just one way to modify the auto-generated email messages and the most likely one to cause errors. Please use this filter with care and keep in mind that we have a wide-variety of magic tags you can use to craft your email messages.
The pattern you use must use %s twice. The first will be filled with the field’s label. The second will be replaced with the field’s value.
Where Does This Code Go?
When using WordPress hooks to customize Caldera Forms or other plugins you should not modify the plugin files, or you will lose your changes when you update the plugin. Instead you should create a small plugin to hold the custom code. It's easy, learn how here.
Technically you can add the custom code to your theme's functions.php, but then you will not be able to change your theme and keep these customizations.