Package rootcerts provides an embedded copy of the "Mozilla Included CA Certificate List" (https://wiki.mozilla.org/CA/Included_Certificates), more specifically the "PEM of Root Certificates in Mozilla's Root Store with the Websites (TLS/SSL) Trust Bit Enabled" (https://ccadb-public.secure.force.com/mozilla/IncludedRootsPEMTxt?TrustBitsInclude=Websites). The "Mozilla Included CA Certificate List" is maintained as part of the Common CA Database effort (https://golang.org/pkg/crypto/x509/). If this package is imported anywhere in the program, then if the crypto/x509 package cannot find the system certificate pool, it will use this embedded information. Additionally, the usage of this embedded information can be forced by setting the the environment variable `GO_ROOTCERTS_ENABLE=1` while running a program, which includes this package. Importing this package will increase the size of a program by about 250 KB. This package should normally be imported by a program's main package, not by a library. Libraries normally shouldn't decide whether to include the "Mozilla Included CA Certificate List" in a program.