function startSession($pkg, $contents, $dest)
    {
        $subst_from = $subst_to = array();
        foreach ($this->_replacements as $a) {
            $a = $a['attribs'];
            $to = '';
            if ($a['type'] == 'pear-config') {
                if ($this->installphase == PEAR_TASK_PACKAGE) {
                    return false;
                }
                if ($a['to'] == 'master_server') {
                    $chan = $this->registry->getChannel($pkg->getChannel());
                    if (!PEAR::isError($chan)) {
                        $to = $chan->getServer();
                    } else {
                        $this->logger->log(0, "$dest: invalid pear-config replacement: $a[to]");
                        return false;
                    }
                } else {
                    if ($this->config->isDefinedLayer('ftp')) {
                        // try the remote config file first
                        $to = $this->config->get($a['to'], 'ftp', $pkg->getChannel());
                        if (is_null($to)) {
                            // then default to local
                            $to = $this->config->get($a['to'], null, $pkg->getChannel());
                        }
                    } else {
                        $to = $this->config->get($a['to'], null, $pkg->getChannel());
                    }
                }
                if (is_null($to)) {
                    $this->logger->log(0, "$dest: invalid pear-config replacement: $a[to]");
                    return false;
                }
            } elseif ($a['type'] == 'php-const') {
                if ($this->installphase == PEAR_TASK_PACKAGE) {
                    return false;
                }
                if (defined($a['to'])) {
                    $to = constant($a['to']);
                } else {
                    $this->logger->log(0, "$dest: invalid php-const replacement: $a[to]");
                    return false;
                }
            } else {
                if ($t = $pkg->packageInfo($a['to'])) {
                    $to = $t;
                } else {
                    $this->logger->log(0, "$dest: invalid package-info replacement: $a[to]");
                    return false;
                }
            }
            if (!is_null($to)) {
                $subst_from[] = $a['from'];
                $subst_to[] = $to;
            }
        }
        $this->logger->log(3, "doing " . sizeof($subst_from) .
            " substitution(s) for $dest");
        if (sizeof($subst_from)) {
            $contents = str_replace($subst_from, $subst_to, $contents);
        }
        return $contents;
    }