get_search_form heredoc.php

<?php 

function philosophy_search_form( $form ) {
    $homedir      = home_url( "/" );
    $label        = __( "Search for:", "philosophy" );
    $button_label = __( "Search", "philosophy" );
    $post_type    = <<<PT
<input type="hidden" name="post_type" value="post">
PT;

    if ( is_post_type_archive( 'book' ) ) {  // book is a post type
        $post_type = <<<PT
<input type="hidden" name="post_type" value="book">
PT;
    }


    $newform = <<<FORM
<form role="search" method="get" class="header__search-form" action="{$homedir}">
    <label>
        <span class="hide-content">{$label}</span>
        <input type="search" class="search-field" placeholder="Type Keywords" value="" name="s"
               title="{$label}" autocomplete="off">
    </label>
    {$post_type}
    <input type="submit" class="search-submit" value="{$button_label}">
</form>
FORM;

    return $newform;
}


add_filter( "get_search_form", "philosophy_search_form" );