When called with just a context, PackageImport behaves like Needs:

An important feature of PackageImport is that it allows "import by name" of only specific symbols from an external package. This feature of importing only a subset of symbols requires that PackageImport is called from a file in a package that uses the Structured Package Format.

The PackageImportExample directory in ExampleData contains a simple package in the Structured Package Format (SPF) style. This is the contents of the WolframMark.wl file from the package, which defines a WolframMark function:

PackageImport["Benchmarking`", Benchmark]

PackageExported[WolframMark]

WolframMark[] :=
    Module[{bench},
        bench = First[Benchmark[]];
        {"WolframMark" -> "BenchmarkResult" /. bench, "DetailedResults" -> BenchmarkReport[bench]}
    ]

BenchmarkReport[bench_] := "Results" /. bench

This package uses functions from the standard Benchmarking` package, so it calls PackageImport to load that package and make its symbols visible within the file. The symbol you will want to use from the Benchmarking` package is Benchmark, but the Benchmarking` package also exports a BenchmarkReport function, which happens to conflict with a BenchmarkReport function that is already defined as a local function within the WolframMark.wl file. To solve this problem, the file calls PackageImport["Benchmarking`",Benchmark] to import only the Benchmark symbol.

To use this example, first add its parent directory to $Path so that it can be found via a context name:

Now load the package in the usual way:

The function works as expected, showing that the BenchmarkReport function used is the one defined in the file, not the one from the Benchmarking` package:

It is an error to call PackageImport for a symbol that does not exist in the imported package. Create a temporary package file and use PackageInitialize to load it as a package:

PackageImport works with context aliases in the same way Needs does.

Read in the Computer Arithmetic package with the alias ca`:

Symbols can be accessed using the context alias:

The package's actual context, ComputerArithmetic`, is not added to $ContextPath when an alias is specified:

If you have external contexts that need to be made visible in all files of your package, you can either put a PackageImport call into every file or use the "HiddenImports" property in your PackageInitialize call:

PackageInitialize["MyPackage`", <|"HiddenImports" -> {"SomeOtherContext`"}|>]