PHPePub\Core\EPub::processCSSExternalReferences PHP Method

    protected function processCSSExternalReferences(&$cssFile, $externalReferences = EPub::EXTERNAL_REF_ADD, $baseDir = "", $cssDir = "")
    {
        if ($this->isFinalized || $externalReferences === EPub::EXTERNAL_REF_IGNORE) {
            return false;
        }
        $backPath = preg_replace('#[^/]+/#i', "../", $cssDir);
        $imgs = null;
        preg_match_all('#url\\s*\\([\'\\"\\s]*(.+?)[\'\\"\\s]*\\)#im', $cssFile, $imgs, PREG_SET_ORDER);
        $itemCount = count($imgs);
        for ($idx = 0; $idx < $itemCount; $idx++) {
            $img = $imgs[$idx];
            if ($externalReferences === EPub::EXTERNAL_REF_REMOVE_IMAGES || $externalReferences === EPub::EXTERNAL_REF_REPLACE_IMAGES) {
                $cssFile = str_replace($img[0], "", $cssFile);
            } else {
                $source = $img[1];
                $pathData = pathinfo($source);
                $internalSrc = $pathData['basename'];
                $internalPath = "";
                $isSourceExternal = false;
                if ($this->resolveImage($source, $internalPath, $internalSrc, $isSourceExternal, $baseDir, $cssDir)) {
                    $cssFile = str_replace($img[0], "url('" . $backPath . $internalPath . "')", $cssFile);
                } elseif ($isSourceExternal) {
                    $cssFile = str_replace($img[0], "", $cssFile);
                    // External image is missing
                }
                // else do nothing, if the image is local, and missing, assume it's been generated.
            }
        }
        return true;
    }