* Default constructor.
     */
    public NotificationHelper() {
        // Default constructor
    }

    private static final Logger logger = LogManager.getLogger(NotificationHelper.class);

    /** Line feed character for message formatting. */
    protected static final char LF = '\n';

    /**
     * Sends notifications to configured platforms.
     *
     * @param cardView the card view for the notification

     *
     * This method removes characters that are not allowed in XML documents
     * according to the XML 1.0 specification. Valid characters include:
     * - Tab (0x9)
     * - Line feed (0xA)
     * - Carriage return (0xD)
     * - Any character between 0x20 and 0xD7FF
     * - Any character between 0xE000 and 0xFFFD
     * - Any character between 0x10000 and 0x10FFFF
     *

## Advanced description from docstring { #advanced-description-from-docstring }

You can limit the lines used from the docstring of a *path operation function* for OpenAPI.

Adding an `\f` (an escaped "form feed" character) causes **FastAPI** to truncate the output used for OpenAPI at this point.

It won't show up in the documentation, but other tools (such as Sphinx) will be able to use the rest.

            protected PathMappingHelper getPathMappingHelper() {
                return new PathMappingHelper();
            }
        };
        fessXpathTransformer.init();
        fessXpathTransformer.convertUrlMap.put("feed:", "http:");

        List<RequestData> urlList = new ArrayList<>();

        urlList = fessXpathTransformer.convertChildUrlList(urlList);
        assertEquals(0, urlList.size());

        urlList.clear();

 *       {@code Number}, and primitive varargs are supported.
 *   <li>Or, to avoid storing up all the data first, create a {@link StatsAccumulator} instance,
 *       feed values to it as you get them, then call {@link StatsAccumulator#snapshot}.
 * </ul>
 *
 * <p>Static convenience methods called {@code meanOf} are also provided for users who wish to
 * calculate <i>only</i> the mean.
 *

* `$`: ends there, doesn't have any more characters after `fixedquery`.

If you feel lost with all these **"regular expression"** ideas, don't worry. They are a hard topic for many people. You can still do a lot of stuff without needing regular expressions yet.

Now you know that whenever you need them you can use them in **FastAPI**.

# Environment Variables { #environment-variables }

/// tip

If you already know what "environment variables" are and how to use them, feel free to skip this.

///

An environment variable (also known as "**env var**") is a variable that lives **outside** of the Python code, in the **operating system**, and could be read by your Python code (or by other programs as well).

///

## Write the callback documentation code { #write-the-callback-documentation-code }

This code won't be executed in your app, we only need it to *document* how that *external API* should look like.

But, you already know how to easily create automatic documentation for an API with **FastAPI**.

func randomizeBytes(s []byte, seed int64) []byte {
	// special value -1 means no explicit seeding.
	if seed != -1 {
		rand.Seed(seed)
	}
	n := len(s)
	var j int
	for i := 0; i < n-1; i++ {
		j = i + rand.Intn(n-i)
		s[i], s[j] = s[j], s[i]
	}
	return s
}

func TestToErrIsNil(t *testing.T) {
	if toObjectErr(nil) != nil {

browser --> proxy
proxy --> server
```

/// tip

The IP `0.0.0.0` is commonly used to mean that the program listens on all the IPs available in that machine/server.

///

The docs UI would also need the OpenAPI schema to declare that this API `server` is located at `/api/v1` (behind the proxy). For example:

```JSON hl_lines="4-8"
{
    "openapi": "3.1.0",
    // More stuff here
    "servers": [
        {