Allow Inline SVG in WordPress Content Editor

By default, WordPress does not allow all types of code in the WordPress content editor. For example, Inline SVGs contain many tags such as <def>, <rect>, etc. To allow Inline SVG, use the following code in functions.php:

function override_mce_options($initArray) {
    $opts = '*[*]';
    $initArray['valid_elements'] = $opts;
    $initArray['extended_valid_elements'] = $opts;
    return $initArray;
}
add_filter('tiny_mce_before_init', 'override_mce_options');

Note that this code allows any tag, whether SVG-related or not.