// Allows for a sub-match of the first value after 'for=' to the next
	// comma, semi-colon or space. The match is case-insensitive.
	forRegex = regexp.MustCompile(`(?i)(?:for=)([^(;|,| )]+)(.*)`)
	// Allows for a sub-match for the first instance of scheme (http|https)
	// prefixed by 'proto='. The match is case-insensitive.
	protoRegex = regexp.MustCompile(`(?i)^(;|,| )+(?:proto=)(https|http)`)
)

    @Throws(IOException::class)
    fun parse(responseHeaders: Headers): WebSocketExtensions {
      // Note that this code does case-insensitive comparisons, even though the spec doesn't specify
      // whether extension tokens and parameters are case-insensitive or not.

      var compressionEnabled = false
      var clientMaxWindowBits: Int? = null
      var clientNoContextTakeover = false

package okhttp3.internal.http2

import okio.ByteString
import okio.ByteString.Companion.encodeUtf8

/** HTTP header: the name is an ASCII string, but the value can be UTF-8. */
data class Header(
  /** Name in case-insensitive ASCII encoding. */
  @JvmField val name: ByteString,
  /** Value in UTF-8 encoding. */
  @JvmField val value: ByteString,
) {
  @JvmField val hpackSize = 32 + name.size + value.size

So, by default, `Header` will convert the parameter names characters from underscore (`_`) to hyphen (`-`) to extract and document the headers.

Also, HTTP headers are case-insensitive, so, you can declare them with standard Python style (also known as "snake_case").

		etag = metadata["md5Sum"]
	}
	// Success.
	return etag
}

// HasPrefix - Prefix matcher string matches prefix in a platform specific way.
// For example on windows since its case insensitive we are supposed
// to do case insensitive checks.
func HasPrefix(s string, prefix string) bool {
	if runtime.GOOS == globalWindowsOSName {
		return stringsHasPrefixFold(s, prefix)
	}
	return strings.HasPrefix(s, prefix)
}

        checkVersionsEqual("1a1", "1-alpha-1");
        checkVersionsEqual("1b2", "1-beta-2");
        checkVersionsEqual("1m3", "1-milestone-3");

        // case insensitive
        checkVersionsEqual("1X", "1x");
        checkVersionsEqual("1A", "1a");
        checkVersionsEqual("1B", "1b");
        checkVersionsEqual("1M", "1m");
        checkVersionsEqual("1Cr", "1Rc");

      pattern += "."
    }
    // Hostname and pattern are now absolute domain names.

    pattern = pattern.asciiToLowercase()
    // Hostname and pattern are now in lower case -- domain names are case-insensitive.

    if ("*" !in pattern) {
      // Not a wildcard pattern -- hostname and pattern must match exactly.
      return hostname == pattern
    }

    // Wildcard pattern

 * <li>version components in the text can be digits or strings,</li>
 * <li>strings are checked for well-known qualifiers and the qualifier ordering is used for version ordering.
 *     Well-known qualifiers (case insensitive) are:<ul>
 *     <li><code>alpha</code> or <code>a</code></li>
 *     <li><code>beta</code> or <code>b</code></li>
 *     <li><code>milestone</code> or <code>m</code></li>
 *     <li><code>rc</code> or <code>cr</code></li>

  fun name(index: Int): String = commonName(index)

  /** Returns the value at `index`. */
  fun value(index: Int): String = commonValue(index)

  /** Returns an immutable case-insensitive set of header names. */
  fun names(): Set<String> {
    val result = TreeSet(String.CASE_INSENSITIVE_ORDER)
    for (i in 0 until size) {
      result.add(name(i))
    }

///

Then, when you create an instance of that `Settings` class (in this case, in the `settings` object), Pydantic will read the environment variables in a case-insensitive way, so, an upper-case variable `APP_NAME` will still be read for the attribute `app_name`.