function initializeFlow(effects) {
  const self = this
  const initial = effects.attempt(
    // Try to parse a blank line.
    blankLine,
    atBlankEnding,
    // Try to parse initial flow (essentially, only code).
    effects.attempt(
      this.parser.constructs.flowInitial,
      afterConstruct,
      factorySpace(
        effects,
        effects.attempt(
          this.parser.constructs.flow,
          afterConstruct,
          effects.attempt(content, afterConstruct)
        ),
        types.linePrefix
      )
    )
  )

  return initial

  /** @type {State} */
  function atBlankEnding(code) {
    assert(
      code === codes.eof || markdownLineEnding(code),
      'expected eol or eof'
    )

    if (code === codes.eof) {
      effects.consume(code)
      return
    }

    effects.enter(types.lineEndingBlank)
    effects.consume(code)
    effects.exit(types.lineEndingBlank)
    self.currentConstruct = undefined
    return initial
  }

  /** @type {State} */
  function afterConstruct(code) {
    assert(
      code === codes.eof || markdownLineEnding(code),
      'expected eol or eof'
    )

    if (code === codes.eof) {
      effects.consume(code)
      return
    }

    effects.enter(types.lineEnding)
    effects.consume(code)
    effects.exit(types.lineEnding)
    self.currentConstruct = undefined
    return initial
  }
}
@this {TokenizeContext}
  Self.
@type {Initializer}
  Initializer.