src/Zend/Filter/StringTrim.php
public function filter($value)
    {
        if (null === $this->_charList) {
            return $this->_unicodeTrim((string) $value);
        } else {
            return $this->_unicodeTrim((string) $value, $this->_charList);
        }
    }
public function filter($value)
    {
        if (null === $this->_charList) {
            return $this->_unicodeTrim((string) $value);
        } else {
            return $this->_unicodeTrim((string) $value, $this->_charList);
        }
    }
Defined by Zend_Filter_Interface

Returns the string $value with characters stripped from the beginning and end

@param  string $value
@return string