src/Zend/Filter/HtmlEntities.php
public function filter($value)
    {
        $filtered = htmlentities((string) $value, $this->getQuoteStyle(), $this->getEncoding(), $this->getDoubleQuote());
        if (strlen((string) $value) && !strlen($filtered)) {
            if (!function_exists('iconv')) {

                throw new Zend_Filter_Exception('Encoding mismatch has resulted in htmlentities errors');
            }
            $enc      = $this->getEncoding();
            $value    = iconv('', $enc . '//IGNORE', (string) $value);
            $filtered = htmlentities($value, $this->getQuoteStyle(), $enc, $this->getDoubleQuote());
            if (!strlen($filtered)) {

                throw new Zend_Filter_Exception('Encoding mismatch has resulted in htmlentities errors');
            }
        }
        return $filtered;
    }
public function filter($value)
    {
        $filtered = htmlentities((string) $value, $this->getQuoteStyle(), $this->getEncoding(), $this->getDoubleQuote());
        if (strlen((string) $value) && !strlen($filtered)) {
            if (!function_exists('iconv')) {

                throw new Zend_Filter_Exception('Encoding mismatch has resulted in htmlentities errors');
            }
            $enc      = $this->getEncoding();
            $value    = iconv('', $enc . '//IGNORE', (string) $value);
            $filtered = htmlentities($value, $this->getQuoteStyle(), $enc, $this->getDoubleQuote());
            if (!strlen($filtered)) {

                throw new Zend_Filter_Exception('Encoding mismatch has resulted in htmlentities errors');
            }
        }
        return $filtered;
    }
Defined by Zend_Filter_Interface

Returns the string $value, converting characters to their corresponding HTML entity
equivalents where they exist

@param  string $value
@return string