function clear_text_field(field_id){
	text_user_email=document.getElementById(field_id).value;
	if(text_user_email == 'Votre E-mail')
	{
		document.getElementById(field_id).value='';
	}
	else if (text_user_email == 'Votre code postal')
	{
		document.getElementById(field_id).value='';
	}
}