WP calendar summary attribute validation error

Update to 3.2.2. The summary attribute has been removed. See line 1149 \wp-includes\general-template.php

WP v3.1.4:

$calendar_output="<table id="wp-calendar" summary="" . esc_attr__('Calendar') . '">

WP v3.2.2:

$calendar_output="<table id="wp-calendar">

Alternatives… To modify the output of the widget, you can duplicate it and rename it. When I did that, I also needed to duplicate the get_calendar() function and adjust the calls to apply_filters() and the caching functions. It was worth the work, because I wanted complete control of the calendar widget”s output.

Another approach is to use the get_calendar filter and modify the output using str_replace, simple xml, regex, etc. Here’s a solution using str_replace() (add this code to functions.php):

add_filter( 'get_calendar', 'customize_calendar_output' );
function customize_calendar_output( $calendar_output ) {
    $calendar_output = str_replace( '<table id="wp-calendar" summary="' . esc_attr__('Calendar') . '">', '<table id="wp-calendar">', $calendar_output );
    return $calendar_output;
}