Properties do not have to be prepended with a hash (#) character, the hash character will be automatically added to the custom properties.These properties and callbacks are not allowed: #allowed_tags, #tree, #array_parents, #parents, #weight, #access_callback, #ajax, #after_build, #element_validate, #lazy_builder, #post_render, #pre_render, #process, #submit, #validate, #value_callback, #file_value_callbacks, #date_date_callbacks, #date_time_callbacks, and #captcha_validate