These functions are not documented. They are basically internal ACF functions that I know about from digging around in the code. This is how ACF gets the field groups and fields. Using them at the wrong time can also cause issues if you’re not careful. In particular, if you want to change the settings of a field group or field after you’ve called these functions you’ll need to manually clear the cached versions. These functions store the results in a cache so that the fields do not need to be retrieved from the database again. But since the values are cached any changes to them are not updated.
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