CoreFilters

The CoreFilters set contains filters that Google's PageSpeed team believes are safe for most web sites. By using the CoreFilters set, as PageSpeed is updated with new filters, your site will get faster.

The core set of filters contains:

add_head combine_css combine_javascript convert_meta_tags extend_cache fallback_rewrite_css_urls flatten_css_imports inline_css inline_import_to_link inline_javascript rewrite_css rewrite_images rewrite_javascript rewrite_style_attributes_with_url

Configuration

Enable pagespeed RewriteLevel CoreFilters (default)
Disable pagespeed RewriteLevel PassThrough