Source

File: wp-includes/general-template.php

function user_can_richedit() {
	global $wp_rich_edit, $is_gecko, $is_opera, $is_safari, $is_chrome, $is_IE, $is_edge;

	if ( ! isset( $wp_rich_edit ) ) {
		$wp_rich_edit = false;

		if ( 'true' === get_user_option( 'rich_editing' ) || ! is_user_logged_in() ) { // Default to 'true' for logged out users.
			if ( $is_safari ) {
				$wp_rich_edit = ! wp_is_mobile() || ( preg_match( '!AppleWebKit/(\d+)!', $_SERVER['HTTP_USER_AGENT'], $match ) && intval( $match[1] ) >= 534 );
			} elseif ( $is_IE ) {
				$wp_rich_edit = ( strpos( $_SERVER['HTTP_USER_AGENT'], 'Trident/7.0;' ) !== false );
			} elseif ( $is_gecko || $is_chrome || $is_edge || ( $is_opera && ! wp_is_mobile() ) ) {
				$wp_rich_edit = true;
			}
		}
	}

	/**
	 * Filters whether the user can access the visual editor.
	 *
	 * @since 2.1.0
	 *
	 * @param bool $wp_rich_edit Whether the user can access the visual editor.
	 */
	return apply_filters( 'user_can_richedit', $wp_rich_edit );
}