_edd_deprected_argument() – Marks an argument in a function deprecated and informs when it’s been used
ArrayToXML::isAssoc() – Check if array is associative with string based keys FROM: http://stackoverflow.com/questions/173400/php-arrays-a-good-way-to-check-if-an-array-is-associative-or-sequential/4254008#4254008
ArrayToXML::writeAttr() – Write keys in $data prefixed with @ as XML attributes, if $data is an array.
edd_add_customer_email() – Add an email address to the customer from within the admin and log a customer note
edd_add_options_link() – Creates the admin submenu pages under the Downloads menu and assigns their links to global variables
