$post_id = get_the_ID();
$user = wp_get_current_user();
$user_identity = $user->exists() ? $user->display_name : '';
$size="30"; //input field size in chars
$commenter = wp_get_current_commenter();
$req      = get_option( 'require_name_email' );
$html_req = ( $req ? " required='required'" : '' );
$html5    = current_theme_supports( 'html5', 'comment-form' ) ? 1 : 0;
$consent  = empty( $commenter['comment_author_email'] ) ? '' : ' checked="checked"';
//ref: functions.php  -> add_filter( 'comment_form_defaults', 'rtf_comment_form' )
$comment_args = array(
    //'format' => 'xhtml',
    'class_form' => 'comment-form needs-validation', //Bootstrap 4 validation
    'class_submit' => 'submit btn btn-default', //Bootstrap 4 button
    'comment_field' =>
        '<div class="comment-form-comment form-group">
            <label for="comment" class="required">' . _x( 'Comment', 'noun' ).'</label>
            <textarea class="form-control" id="comment" name="comment" cols="45" rows="6" maxlength="65525" aria-describedby="form-allowed-tags"' . $html_req . '></textarea>display-kubuntu-kde-versions/
            <div class="invalid-feedback">
                Fill out comment
            </div>
        </div>',
    'fields' => array(
        'author' =>
            '<div class="comment-form-author form-group">
                <label for="author" class="required">' . __( 'Name' ).'</label>
                <input class="form-control" id="author" name="author" type="text" value="' . esc_attr( $commenter['comment_author'] ) . '" size="'.$size.'" maxlength="245"' . $html_req . '/>
                <div class="invalid-feedback">
                    Enter name
                </div>
            </div>',
        'email' =>
            '<div class="comment-form-email form-group">
                <label for="email" class="required">' . __( display-kubuntu-kde-versions/'Email' ).'</label>
                <input class="form-control" id="email" name="email" aria-describedby="email-notes" ' . ( $html5 ? 'type="email"' : 'type="text"' ) . ' value="' . esc_attr( $commenter['comment_author_email'] ) . '" size="'.$size.'" maxlength="100"' . $html_req . '/>
                <div class="invalid-feedback">
                    Enter valid email
                </div>
            </div>',
        'url' =>
            '<div class="comment-form-url form-group">
                <label for="url">' . __( 'Website' ) . '</label>
                <input class="form-control" id="url" name="url" ' . ( $html5 ? 'type="url"' : 'type="text"' ) . ' value="' . esc_attr( $commenter['comment_author_url'] ) . '" size="'.$size.'" maxlength="200" />display-kubuntu-kde-versions/
                <div class="invalid-feedback">
                    Enter valid web address (url)
                </div>
            </div>',
        'cookies' =>
            '<div class="comment-form-cookies-consent form-group">
                <input id="wp-comment-cookies-consent" name="wp-comment-cookies-consent" type="checkbox" value="yes"' . $consent . display-kubuntu-kde-versions/' />' . '<label for="wp-comment-cookies-consent">' .'&nbsp'.  __( 'Save my name, email, and website in this browser for the next time I comment.' ) . '</label>
            </div>',
    ),
);
comment_form($comment_args);

//Set wp_editor Comment(textarea) defaults: no statusbar, no Text tab, fullscreen; body_class= form-control (bs4)
add_filter( 'comment_form_defaults', 'rtf_comment_form' );
function rtf_comment_form( $args ) {
global $root; //theme root directory
$time = time();
ob_start();
wp_editor( '','comment', array( //Initial_content,comment_html_id, editor_settings
    //'skin' => 'lightgray',
    'quicktags' => false, //disable Text tab
    //'teeny' => true,
    //'quicktags' => array('buttons' => 'strong,em,link,block,del,ins,img,ul,ol,li,code,close'),
    //'dfw' => false, // replace the default full screen with DFW (WordPress 3.4+)
    'tinymce'       => array(
        //'selector' => 'textarea', //textarea default
        //'toolbar1' => 'fontselect,fontsizeselect,|,bold,italic,underline,strikethrough,bullist,numlist,code,outdent,indent,|,undo,redo',
        //'toolbar2' => '',
        'statusbar' => false, // remove html tags like p at bottom
        //'fontsize_formats' => '15pt 18pt 24pt 48pt', // overrride tinymce font pull-down
        //'content_css' => $root.'/css/style.css?'. $time, //set pcd theme style + fix cache issue - force page reload by adding bogus time
        //'body_class' => 'form-control', //Bootstrap4 to ensure comment textarea like input fields
        //'skin' => 'lightgray',//default
        //'skin' => 'wordpress',
        //'theme' => 'modern', //default
        //'theme_advanced_disable' => 'fullscreen',
    )
)
);
$args['comment_field'] = ob_get_clean();
return $args;