Overview of error message improvements

gistfile1.php

<?php
// Example of adding an error to the edd_set_error
/**
 * Checks whether a discount code is active.
 *
 * @since 1.0
 * @param int $code_id
 * @return bool
 */
function edd_is_discount_active( $code_id = null ) {
	$discount = edd_get_discount( $code_id );
	$return   = false;

	if ( $discount ) {
		if ( $discount->post_status == 'active' && ! edd_is_discount_expired( $code_id ) ) {
			$return = true;
		} else {
			edd_set_error( 'edd-discount-error', __( 'This discount is not active.', 'edd' ) );
		}
	}

	return apply_filters( 'edd_is_discount_active', $return, $code_id );
}

// In the ajax-functions.php, instead of just returning the generic message if the response is false we use this
$errors = edd_get_errors();
$return['msg']  = $errors['edd-discount-error'];
edd_unset_error( 'edd-discount-error' ); // This helps with the UX when trying multiple codes

// For the display, it was as simple as adding a line after the discount code input
// Display none since we don't need it yet, ID for targeting (better performance) and class for stlye (repeatable)
<input class="edd-input" type="text" id="edd-discount" name="edd-discount" placeholder="<?php _e( 'Enter discount', 'edd' ); ?>"/>
<span id="edd-discount-error-wrap" class="edd-discount-error" style="display:none;"></span>

// In the edd-checkout-global.js we make an addition to reset that span
$('#edd-discount-error-wrap').html('').hide();
// And then 1 modification to what we're putting into the span (instead of the alert())
$('#edd-discount-error-wrap').html(discount_response.msg).show();

// and in the edd.css under the 'Checkout Fields' section, a HUGE addition
.edd-discount-error { color: #F33; }