## Documenting the callback { #documenting-the-callback }

The actual callback code will depend heavily on your own API app.

And it will probably vary a lot from one app to the next.

It could be just one or two lines of code, like:

```Python
callback_url = "https://example.com/api/v1/invoices/events/"
httpx.post(callback_url, json={"description": "Invoice paid", "paid": True})
```

func (kv *BatchJobKV) UnmarshalYAML(val *yaml.Node) error {
	type jobKV BatchJobKV
	var tmp jobKV
	err := val.Decode(&tmp)
	if err != nil {
		return err
	}
	*kv = BatchJobKV(tmp)
	kv.line, kv.col = val.Line, val.Column
	return nil
}

// Validate returns an error if key is empty
func (kv BatchJobKV) Validate() error {
	if kv.Key == "" {
		return BatchJobYamlErr{
			line: kv.line,

        String line;
        final BufferedReader br = new BufferedReader(r);

        while ((line = br.readLine()) != null) {
            line = line.toUpperCase().trim();
            if (line.length() == 0) {
                continue;
            }
            if (line.charAt(0) == '#') {
                if (line.startsWith("#INCLUDE ")) {

	// Output:
	// Original : ahoj vývojári golang
	// ToUpper : AHOJ VÝVOJÁRİ GOLANG
}

func ExampleLines() {
	text := []byte("Hello\nWorld\nGo Programming\n")
	for line := range bytes.Lines(text) {
		fmt.Printf("%q\n", line)
	}

	// Output:
	// "Hello\n"
	// "World\n"
	// "Go Programming\n"
}

func ExampleSplitSeq() {
	s := []byte("a,b,c,d")

/**
 * Parse all headers delimited by "\r\n" until an empty line. This throws if headers exceed 256 KiB.
 */
class HeadersReader(
  val source: BufferedSource,
) {
  private var headerLimit = HEADER_LIMIT.toLong()

  /** Read a single line counted against the header size limit. */
  fun readLine(): String {
    val line = source.readUtf8LineStrict(headerLimit)
    headerLimit -= line.length.toLong()
    return line
  }

    }

    /**
     * Strips comments from a line (everything after '#' character).
     * @param line the line to strip comments from
     * @return the line without comments
     */
    protected String stripComment(final String line) {
        final int commentIndex = line.indexOf('#');
        if (commentIndex != -1) {
            return line.substring(0, commentIndex);
        }
        return line;
    }

    /**
     * Add a header line without any validation. Only appropriate for headers from the remote peer
     * or cache.
     */
    internal fun addLenient(line: String) =
      apply {
        val index = line.indexOf(':', 1)
        when {
          index != -1 -> {
            addLenient(line.substring(0, index), line.substring(index + 1))
          }
          line[0] == ':' -> {

        String line;
        final BufferedReader br = new BufferedReader(r);

        while ((line = br.readLine()) != null) {
            line = line.toUpperCase().trim();
            if (line.length() == 0) {
                continue;
            }
            if (line.charAt(0) == '#') {
                if (line.startsWith("#INCLUDE ")) {

          throw ProtocolException("Unexpected status line: $statusLine")
        }
        val httpMinorVersion = statusLine[7] - '0'
        codeStart = 9
        protocol =
          when (httpMinorVersion) {
            0 -> Protocol.HTTP_1_0
            1 -> Protocol.HTTP_1_1
            else -> throw ProtocolException("Unexpected status line: $statusLine")
          }
      } else if (statusLine.startsWith("ICY ")) {

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