WP validation - options-register.php

<?php
// Register theme_tdg_options array to hold all theme options
register_setting( 'theme_tdg_options', 'theme_tdg_options', 'tdg_validate' );

function tdg_validate( $input ) {
    // default options
    $tdg_default_options = tdg_get_default_options(); # returns an array with the default options as stored initially on the database

    // Determine which form action was submitted
    [...]
    $submit_cart = ( ! empty($input['submit-cart'] ) ? true : false );
    $reset_cart = ( ! empty($input['reset-cart'] ) ? true : false );

    if ( $submit_cart ) { // if cart Settings Submit
        // Cart explanation text
        $input['tdg_cart_explanation'] = ( '' == $input['tdg_cart_explanation'] ? $tdg_default_options['tdg_cart_explanation'] : wp_kses_data($input['tdg_cart_explanation']) );
        // Cart page address
        if( tdg_use_permalink() ) { # true if "pretty" permalinks are active, false otherwise
        $input['tdg_cart_page'] = ( '' == $input['tdg_cart_page'] ? $tdg_default_options['tdg_cart_page'] : sanitize_title($input['tdg_cart_page']) );
        } else {
        $input['tdg_cart_page'] = ( '' == $input['tdg_cart_page'] ? $tdg_default_options['tdg_cart_page'] : intval($input['tdg_cart_page']) );
        }

    } elseif ( $reset_cart ) { // if cart Settings Reset Defaults

        $tdg_default_options = tdg_get_default_options();
        // Cart Explanation text
        $input['tdg_cart_explanation'] = $tdg_default_options['tdg_cart_explanation'];
        // Cart Page address
        $input['tdg_cart_page'] = $tdg_default_options['tdg_cart_page'];

    }
    return $input;

}