Código HTML:
<html> <form name="for_check" method="POST" action="array_checkbox.html"> <ul> <input type='checkbox' name='rubros[1]' value='<?=1?>'>Alimentos<ul> <li><input type='checkbox' name='subrubros[1][2]' value='<?=2?>'>Frutas</li> <li><input type='checkbox' name='subrubros[1][3]' value='<?=3?>'>Verduras</li> </ul> <ul> <input type='checkbox' name='rubros[1]' value='<?=1?>'>Prendas de vestir <li><input type='checkbox' name='subrubros[1][2]' value='<?=2?>'>Vestidos</li> <li><input type='checkbox' name='subrubros[1][3]' value='<?=3?>'>Camisas</li> </ul> <div> <label><input type="submit" value="Enviar"> </label> </div> </form> </html>