Pues sí que valida, pruebalo
Código:
<!DOCTYPE html PUBLIC "-//W3C//DTD XHTML 1.0 Transitional//EN" "http://www.w3.org/TR/xhtml1/DTD/xhtml1-transitional.dtd">
<html xmlns="http://www.w3.org/1999/xhtml">
<head>
<title>Documento sin título</title>
<meta http-equiv="Content-Type" content="text/html; charset=iso-8859-1" />
<script type="text/javascript">
function valida_envia(){
if ((document.cerca.text_titol.value.length==0) || (document.cerca.var_tipologia.value.selectedIndex <= 0) || (document.cerca.var_poblacio.selectedIndex <= 0)) {
alert("Ha de introducir algún criterio de búsqueda");
document.cerca.text_titol.focus()
return false;
}
}
</script>
</head>
<body>
<td height="220"><table width="760">
<td height="151" valign="top"><form id="cerca" name="cerca" action="resul_avancada.php" method="post" onSubmit="return valida_envia()">
<fieldset>
<legend>Cerca avanzada</legend>
<table width="600" border="0" align="center">
<tr>
<td width="150"> </td>
<td colspan="3"> </td>
</tr>
<tr>
<td class="text">Cerca per títol</td>
<td colspan="2" class="text"><input id="text_titol" name="text_titol" type="text" size="50" maxlength="100">
</td>
<td class="text"><strong>Y</strong></td>
</tr>
<tr>
<td class="text">Cercar per tipologia </td>
<td colspan="2" class="text"><select name="var_tipologia" size="1">
<option value="0"></option>
<option value="1">Contes Meravellosos</option>
<option value="2">Contes no Meravellosos</option>
<option value="3">Contes Animalístics</option>
<option value="4">Contes Encadenats</option>
<option value="5">Apòlegs</option>
<option value="6">Tradicions</option>
<option value="7">Bertranades</option>
<option value="8">Rondalles</option>
<option value="9">Antirondalles</option>
<option value="10">Facècies</option>
<option value="11">Llegendes</option>
<option value="12">Història Oral</option>
<option value="13">Teatre</option>
<option value="14">Cançons Infantils</option>
<option value="15">Jocs d'Infants</option>
<option value="16">Folies</option>
<option value="17">Romanços</option>
<option value="18">Tirallongues Toponímiques</option>
<option value="19">Oracions i Cançons Religioses</option>
<option value="20">Cançons de Ball</option>
<option value="21">Refranyer</option>
<option value="22">Enigmística</option>
<option value="23">Mimologia</option>
<option value="24">Tornaveus</option>
<option value="25">Embarbussaments</option>
<option value="26">Enganyalls</option>
<option value="27">Frases Fetes i Locucions</option>
<option value="28">Altres Composicions</option>
</select></td>
<td class="text"><strong>Y</strong></td>
</tr>
<tr>
<td class="text">Cercar por població</td>
<td colspan="2"><select name="var_poblacio" size="1">
<option value="0"></option>
<option value="1">Aiguaviva</option>
<option value="2">Arenys de Lledo</option>
<option value="3">Bellmunt de Mesquí</option>
<option value="4">Beseit</option>
<option value="5">La Canyada de Beric</option>
<option value="6">Calaceit</option>
<option value="7">La Codonyera</option>
<option value="8">Cretes</option>
<option value="9">Faió</option>
<option value="10">Favara de Matarranya</option>
<option value="11">Fontdespatla</option>
<option value="12">Fórnols</option>
<option value="13">La Freixneda</option>
<option value="14">La Ginebrosa</option>
<option value="15">Herbers</option>
<option value="16">Lledó</option>
<option value="17">Maella</option>
<option value="18">El Mas de Llaurador</option>
<option value="19">Massalió</option>
<option value="20">Mequinensa</option>
<option value="21">Mont-roig</option>
<option value="22">Nonasp</option>
<option value="23">La Pobleta de Morella</option>
<option value="24">La Portellada</option>
<option value="25">Pena-roja</option>
<option value="26">Ràfels</option>
<option value="27">La Sorollera</option>
<option value="28">Torredarques</option>
<option value="29">La Torre del Compte</option>
<option value="30">La Torre de Vilella</option>
<option value="31">Valljunquera</option>
<option value="32">La Vall del Tormo</option>
<option value="33">Vall-de-roures</option>
</select></td>
<td> </td>
</tr>
<tr>
<td class="text"> </td>
<td width="155"><input type="submit" name="Submit" value="Cercar"></td>
<td width="155"><input type="reset" name="Submit2" value="Esborrar"></td>
<td width="124"> </td>
</tr>
</table>
</fieldset>
</form>
</body>
</html>