Adds checkbox to limit to Title search

searchform.php

<form role="search" method="get" class="search-form" action="<?php echo home_url( '/' ); ?>">
    <label>
        <span class="screen-reader-text"><?php echo _x( 'Search for:', 'label' ) ?></span>
        <p>
            <input type="checkbox" name="searchwp_limit_to_title" id="searchwp_limit_to_title" value="1" <?php if ( ! empty( $_REQUEST['searchwp_limit_to_title'] ) ) : ?>checked="checked"<?php endif; ?> />
            <label for="searchwp_limit_to_title"><?php esc_html_e( 'Limit to Titles', 'searchwp_child_theme' ); ?></label>
        </p>
        <input type="search" class="search-field"
            placeholder="<?php echo esc_attr_x( 'Search …', 'placeholder' ) ?>"
            value="<?php echo get_search_query() ?>" name="s"
            title="<?php echo esc_attr_x( 'Search for:', 'label' ) ?>" />
    </label>
    <input type="submit" class="search-submit"
        value="<?php echo esc_attr_x( 'Search', 'submit button' ) ?>" />
</form>