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add_filter( 'get_product_search_form' , 'woo_custom_product_searchform' );

/**
 * woo_custom_product_searchform
 *
 * @access      public
 * @since       1.0 
 * @return      void
*/
function woo_custom_product_searchform( $form ) {
	
	$form = '<form role="search" method="get" id="searchform" action="' . esc_url( home_url( '/'  ) ) . '">
		<div>
			<label class="screen-reader-text" for="s">' . __( 'Search for:', 'woocommerce' ) . '</label>
			<input type="text" value="' . get_search_query() . '" name="s" id="s" placeholder="' . __( 'My Search form', 'woocommerce' ) . '" />
			<input type="submit" id="searchsubmit" value="'. esc_attr__( 'Search', 'woocommerce' ) .'" />
			<input type="hidden" name="post_type" value="product" />
		</div>
	</form>';
	
	return $form;
	
}