How does Metacello check for installed packages in the image?

Hi,

I have a Pharo 6.1 image with packages loaded manually (without
BaselineOf or ConfigurationOf). Now if I evaluate a Metacello script
which would install the package already installed in the image (for
example via dependency), is there any check performed against the
RPackages or similar to avoid loading it again?

Cheers,

Hernán