Doc (usually run as go doc) accepts zero, one or two arguments.
Show the documentation for the package in the current directory.
go doc <pkg>
go doc <sym>[.<methodOrField>]
go doc [<pkg>.]<sym>[.<methodOrField>]
go doc [<pkg>.][<sym>.]<methodOrField>
The first item in this list that succeeds is the one whose documentation
is printed. If there is a symbol but no package, the package in the current
directory is chosen. However, if the argument begins with a capital
letter it is always assumed to be a symbol in the current directory.
go doc <pkg> <sym>[.<methodOrField>]
Show the documentation for the package, symbol, and method or field. The
first argument must be a full package path. This is similar to the
command-line usage for the godoc command.
For commands, unless the -cmd flag is present "go doc command"
shows only the package-level docs for the package.
The -src flag causes doc to print the full source code for the symbol, such
as the body of a struct, function or method.
The -all flag causes doc to print all documentation for the package and
all its visible symbols. The argument must identify a package.
For complete documentation, run "go help doc".