<?php
// d.) settings
add_settings_field(
    'woonumday_wndtaxbase_field',
    esc_attr__('Tax Options', 'woonumday'),
    'woonumday_wndtaxbase_field_cb',
    'woonumday_options',
    'woonumday_options_section',
     array(
        'type' => 'select',
        'option_group' => 'woonumday_options',
        'name'         => 'woonumday_wndtaxbase_field',
        'value'        => esc_attr(
                          get_option( 'woonumday_options' )['woonumday_wndtaxbase_field'] ),
        'options'      => array(
                              "standard" => "Standard",
                              "reduced" => "Reduced",
                              "zero" => "Zero" ),
        'description'  => esc_html__( 'This adjust the Additional Fee tax rate only
                                       - not the product tax rate.', 'woonumday' ),
        'tip'  => esc_attr__( 'Choices are: standard | reduced | zero
                              See Woocommerce Settings to set taxes', 'woonumday' )
    )
);

// Callback

/**
 * d.) 'select' field
 * @since 1.0.0
 */
function woonumday_wndtaxbase_field_cb($args)
{
  print('<label for="woonumday_wndtaxbase_field">');
    if( ! empty ( $args['options'] && is_array( $args['options'] ) ) )
    {
    $options_markup = '';
    $value = $args['value'];
        foreach( $args['options'] as $key => $label )
        {
            $options_markup .= sprintf( '<option value="%s" %s>%s</option>',
            $key, selected( $value, $key, false ), $label );
        }
        printf( '<select name="%1$s[%2$s]" id="%1$s-%2$s">%3$s</select>',
        $args['option_group'],
        $args['name'],
        $options_markup );
    }
        $tip = $args['tip'];
        print('<b class="wntip" title="' . esc_attr($tip) . '"> ? </b></label>');
}