Currently the where method of Zend_Db_Select allows to call the where() method with a second parameter that gets quoted substituted into the first parameter and replaces the placeholder (question mark). Since the where() method can be called multiple times, multiple parameters can be quoted.

$select = $db->select()
    ->from("products")
    ->where("product_name = ?", $prod)
    ->where("price < ?", $minimumPrice)
    ->orWhere("price > ?", $maximumPrice);

Unfortunately this usage makes it more difficult when you need to evaluate Boolean expressions in a specific order. In certain cases it becomes necessary to use the non-quoted format in order to clarify the query because AND has higher precedence than OR. Quoting must be done separately.

$minPriceQuoted = $db->quote($minimumPrice);
$maxPriceQuoted = $db->quote($maximumPrice);
$select = $db->select()
    ->from("products")
    ->where("product_name = ?", $prod)
    ->where("price < $minPriceQuoted OR price > $maxPriceQuoted");

If the where() method accepted multiple parameters for quoting, the usage would be much less awkward:

$select = $db->select()
    ->from("products")
    ->where("product_name = ? AND (price < ? OR price > ?)", $prod, $minimumPrice, $maximumPrice);