* creator of the problem, the general expectation is that the hint provides sufficient information to the user to
     * track the problem back to its origin. A concrete example for such a source hint can be the file path or URL from
     * which the settings were read.
     *
     * @return The hint about the source of the problem or an empty string if unknown, never {@code null}.
     */
    String getSource();

    /**

    /**
     * Attaches a produced artifact to the project at the specified path. This is the base method
     * that the other attachArtifact methods delegate to.
     *
     * @param project the project to attach the artifact to
     * @param artifact the produced artifact to attach
     * @param path the path to the artifact file
     * @throws IllegalArgumentException if the project, artifact or path is null
     */

    }

    /**
     * Gets the one-based index of the line containing the error.
     *
     * @return The one-based index of the line containing the error or a non-positive value if unknown.
     */
    public int getLineNumber() {
        return lineNumber;
    }

    /**
     * Gets the one-based index of the column containing the error.
     *

### Include the custom docs

Now you can create the *path operations* for the custom docs.

You can reuse FastAPI's internal functions to create the HTML pages for the docs, and pass them the needed arguments:

* `openapi_url`: the URL where the HTML page for the docs can get the OpenAPI schema for your API. You can use here the attribute `app.openapi_url`.
* `title`: the title of your API.

     * reference. If the cached data is mutable, i.e. could be modified after being put into the cache, the caller is
     * responsible for creating a copy of the original data and store the copy in the cache.
     *
     * @param request The repository request from which this cache was retrieved, must not be {@code null}.
     * @param key The key to use associate the data with, must not be {@code null}.

So, what we will do next is add the code to document how that *external API* should look like to receive the callback from *your API*.

That documentation will show up in the Swagger UI at `/docs` in your API, and it will let external developers know how to build the *external API*.

This example doesn't implement the callback itself (that could be just a line of code), only the documentation part.

/// tip

        "The process cannot access the file because it is being used by another process.",
        "The process cannot access the file because another process has locked a portion of the file.", "The disk is full.",
        "A duplicate name exists on the network.", "The network name cannot be found.", "ERRnomoreconn.", "The file exists.",

        "The process cannot access the file because it is being used by another process.",
        "The process cannot access the file because it is being used by another process.",
        "The process cannot access the file because another process has locked a portion of the file.",
        "The disk is full.",
        "A duplicate name exists on the network.",
        "The network name cannot be found.",

     *
     * @param message The detail message, may be {@code null}.
     * @param groupId The group id of the unresolvable model, may be {@code null}.
     * @param artifactId The artifact id of the unresolvable model, may be {@code null}.
     * @param version The version of the unresolvable model, may be {@code null}.
     * @param cause The cause, may be {@code null}.
     */
    public UnresolvableModelException(

public interface ProjectBuilderResult {

    /**
     * Gets the identifier of the project that could not be built. The general format of the identifier is {@code
     * <groupId>:<artifactId>:<version>} but some of these coordinates may still be unknown at the point the exception
     * is thrown so this information is merely meant to assist the user.
     *
     * @return the identifier of the project or an empty string if not known, never {@code null}
     */