*
   * If this flag is set, the next four
   * bytes represent the mask key. These bytes appear after any additional bytes specified by [B1_MASK_LENGTH].
   */
  internal const val B1_FLAG_MASK = 128

  /**
   * Byte 1 mask for the payload length.
   *
   * If this value is [PAYLOAD_SHORT], the next two
   * bytes represent the length. If this value is [PAYLOAD_LONG], the next eight bytes
   * represent the length.
   */

    var unionWith: Mapping = mapping
    index++

    while (index < mappings.size) {
      val next = mappings[index]

      if (type != canonicalizeType(next.type)) break
      if (type == TYPE_MAPPED && mappedTo != next.mappedTo) break

      unionWith = next
      index++
    }

    result +=
      Mapping(
        sourceCodePoint0 = mapping.sourceCodePoint0,

  private val connectionUser: ConnectionUser,
  private val fastFallback: Boolean,
) {
  // State for negotiating the next proxy to use.
  private var proxies = emptyList<Proxy>()
  private var nextProxyIndex: Int = 0

  // State for negotiating the next socket address to use.
  private var inetSocketAddresses = emptyList<InetSocketAddress>()

  // State for negotiating failed routes

      }
    }

    // Call the next interceptor in the chain.
    val next = copy(index = index + 1, request = request)
    val interceptor = interceptors[index]

    @Suppress("USELESS_ELVIS")
    val response =
      interceptor.intercept(next) ?: throw NullPointerException(
        "interceptor $interceptor returned null",
      )

The main [Tutorial - User Guide](../tutorial/index.md){.internal-link target=_blank} should be enough to give you a tour through all the main features of **FastAPI**.

In the next sections you will see other options, configurations, and additional features.

!!! tip
    The next sections are **not necessarily "advanced"**.

    And it's possible that for your use case, the solution is in one of them.

## Read the Tutorial first

            processor.invoke(symbol.fir)
            ProcessorAction.NEXT
        }
        is FirProperty -> processOverriddenProperties(declaration.symbol) { symbol ->
            processor.invoke(symbol.fir)
            ProcessorAction.NEXT
        }
        else -> ProcessorAction.STOP
    }

    private fun FirTypeScope.processDirectOverriddenDeclarations(

    assertRoute(selection.next(), address, Proxy.NO_PROXY, dns.lookup(uriHost, 0), uriPort)
    assertThat(selection.hasNext()).isFalse()
    assertFailsWith<NoSuchElementException> {
      selection.next()
    }
    assertThat(routeSelector.hasNext()).isFalse()
    assertFailsWith<NoSuchElementException> {
      routeSelector.next()
    }
  }

  @Test fun explicitProxyTriesThatProxysAddressesOnly() {
    val address =

        val hasNext = condition?.calleeReference?.getResolvedSymbolOfNameReference()
        val next = (firLoop.block.statements.firstOrNull() as? FirProperty?)?.getInitializerFunctionCall()
        return listOfNotNull(
            iterator?.fir?.buildSymbol(firSymbolBuilder),
            hasNext?.fir?.buildSymbol(firSymbolBuilder),
            next?.fir?.buildSymbol(firSymbolBuilder),
        )
    }

At the start of a release development cycle, the contents of `next` should be deleted
and replaced with those of `initial`. From the repo root:

    > cd doc
    > rm -r next/*
    > cp -r initial/* next

Then edit `next/1-intro.md` to refer to the next version.

To prepare the release notes for a release, run `golang.org/x/build/cmd/relnote generate`.

the new API. This helps with our end-of-cycle audit of new APIs.
The same requirement applies to next/* (described below), which will
become a go1.XX.txt for XX >= 19.

The next/ directory contains the only files intended to be mutated.
Each file in that directory contains a list of features that may be added
to the next release of Go. The files in this directory only affect the
warning output from the go api tool. Each file should be named