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//////////////////////////////////////////////////////////////
///////// ADD CUSTOM IMAGE SIZES TO WP EDITOR 
//////////////////////////////////////////////////////////////
add_image_size( 'icon100', '100', '100', false );

function my_editor_image_sizes( $sizes ) {
    $sizes = array_merge( $sizes, array(
      'icon100' => __( 'icon 100px' )
    ));
    return $sizes;
}
add_filter( 'image_size_names_choose', 'my_editor_image_sizes' );