I've made a custom module that creates a new field type. Any single-cardinality instances of this field work fine. However, multi-cardinality instances of this field will not pass my #element_validate function; see https://drupal.stackexchange.com/questions/86745/element-validate-function-is-called-on-sub-elements-of-a-form-form-items-are-c
Since I don't need this field to ever be multi-value, I want to disable multiple values for this field entirely.
Is there a way to do this?