#
    variable scriptDirectory; # DEFAULT: <scriptDir>

    if {![info exists scriptDirectory]} then {
      set scriptDirectory $pkgr_path
    }

    #
    # NOTE: This is the name of the executable file used to invoke Fossil,
    #       possibly without a file extension.
    #
    variable fossilFileNameOnly; # DEFAULT: <unset>

    if {![info exists fossilFileNameOnly]} then {
      if {[isWindows]} then {
        set fossilFileNameOnly fossil.exe
      } else {
        set fossilFileNameOnly fossil
      }
    }

    #
    # NOTE: The command to use when attempting to verify that Fossil is
    #       available for use.
    #
    variable fossilVersionCommand; # DEFAULT: fossil version

    if {![info exists fossilVersionCommand]} then {
      set fossilVersionCommand {{${fossilFileNameOnly}} version}
    }

    #
    # NOTE: The regular expression pattern used when attempting to verify
    #       that Fossil is installed.
    #
    variable fossilVersionPattern; # DEFAULT: {^This is fossil version [12]... }

    if {![info exists fossilVersionPattern]} then {
      set fossilVersionPattern {^This is fossil version [12]\.\d+ }
    }

    #
    # NOTE: The command to use when attempting to check for changes prior to
    #       staging files using Fossil.
    #
    variable fossilChangesCommand; # DEFAULT: fossil changes ...

    if {![info exists fossilChangesCommand]} then {
      set fossilChangesCommand \
          {{${fossilFileNameOnly}} changes --chdir {${directory}}}
    }

    #
    # NOTE: The regular expression pattern used when attempting to verify
    #       that the Fossil checkout has no changes staged.  Generally, this
    #       pattern should only match an empty string.
    #
    variable fossilChangesPattern; # DEFAULT: {^$}

    if {![info exists fossilChangesPattern]} then {
      set fossilChangesPattern {^$}
    }

    #
    # NOTE: The command to use when attempting to check the checkout status
    #       prior to staging files using Fossil.
    #
    variable fossilInfoCommand; # DEFAULT: fossil info ...

    if {![info exists fossilInfoCommand]} then {
      set fossilInfoCommand \
          {{${fossilFileNameOnly}} info --chdir {${directory}}}
    }

    #
    # NOTE: The regular expression pattern used when attempting to extract
    #       the current check-in identifier for the Fossil checkout.
    #
    variable fossilInfoCheckoutPattern; # DEFAULT: {^checkout:\s+... UTC$}

    # NOTE: The command to use when attempting to reset the checkout to the
    #       default branch prior to staging files using Fossil.
    #
    variable fossilUpdateCommand; # DEFAULT: fossil update trunk ...

    if {![info exists fossilUpdateCommand]} then {
      set fossilUpdateCommand \
          {{${fossilFileNameOnly}} update trunk --chdir {${directory}}}
    }

    #
    # NOTE: The command to use when attempting to stage package files using
    #       Fossil.
    #
    variable fossilAddCommand; # DEFAULT: fossil add ...

    if {![info exists fossilAddCommand]} then {
      set fossilAddCommand \
          {{${fossilFileNameOnly}} add --chdir {${directory}} {${fileName}}}
    }

    #
    # NOTE: The command to use when attempting to commit package files using
    #       Fossil.
    #
    variable fossilCommitCommand; # DEFAULT: fossil commit ...

    if {![info exists fossilCommitCommand]} then {
      set fossilCommitCommand \
          {{${fossilFileNameOnly}} commit -m {${comment}}\
          --branch {${branch}} --user anonymous --chdir\
          {${directory}} --no-prompt}
    }

    #
    # NOTE: The regular expression pattern used when attempting to verify
    #       that Fossil committed a set of files.
    #


  #
  # NOTE: This procedure attempts to query the identifier of the Fossil
  #       checkout.  There are no arguments.  An empty string is returned if
  #       the information cannot be determined.
  #
  proc getCheckoutId {} {
    variable fossilFileNameOnly
    variable fossilInfoCommand
    variable fossilInfoCheckoutPattern
    variable scriptDirectory

    fossilMustBeInstalled

    if {[isEagle]} then {


  #
  # NOTE: This procedure attempts to query the root directory of the Fossil
  #       checkout.  There are no arguments.  An empty string is returned if
  #       the information cannot be determined.
  #
  proc getCheckoutDirectory {} {
    variable fossilFileNameOnly
    variable fossilInfoCommand
    variable fossilInfoLocalRootPattern
    variable scriptDirectory

    fossilMustBeInstalled

    if {[isEagle]} then {


  #
  # NOTE: This procedure attempts to verify that an implementation of Fossil
  #       is installed locally.  There are no arguments.  Script errors are
  #       raised if any problems are found.  The return value is undefined.
  #
  proc fossilMustBeInstalled {} {
    variable fossilFileNameOnly
    variable fossilVersionCommand
    variable fossilVersionPattern

    set message {
      Cannot use Fossil: it does not appear to be installed.

      Fossil may be downloaded from "https://www.fossil-scm.org/"
      and then installed by copying the (single) Fossil binary to
      a directory that lies somewhere along the executable search
      path.

      Alternatively, it may be possible to install Fossil via the
      package management subsystem included with your operating
      system.
    }

    if {[isEagle]} then {
      if {[catch {
        eval exec -nocarriagereturns -stdout output -stderr error \
            [subst $fossilVersionCommand]
      } result] == 0} then {
        set result [appendArgs $output $error]
      } else {
        error $message
      }
    } else {
      if {[catch {
        eval exec [subst $fossilVersionCommand]
      } result]} then {
        error $message
      }
    }

    if {![info exists result] || \
        ![regexp -- $fossilVersionPattern $result]} then {
      error "cannot use Fossil: unknown or unsupported version"
    }
  }

  #
  # NOTE: This procedure attempts to verify that the checkout directory does
  #       not contain any (stray) changes.  There are no arguments.  Non-zero
  #       is returned if the verification is successful.
  #
  proc verifyThereAreNoChanges {} {
    variable checkoutDirectory
    variable fossilChangesCommand
    variable fossilChangesPattern
    variable fossilFileNameOnly

    fossilMustBeInstalled
    verifyCheckoutDirectory

    if {[isEagle]} then {
      set directory [::PackageRepository::formatExecArgument \
          $checkoutDirectory]


  #
  # NOTE: This procedure attempts to verify that the checkout directory does
  #       belong to the correct project.  There are no arguments.  Non-zero
  #       is returned if the verification is successful.
  #
  proc verifyThisIsTheCorrectProject {} {
    variable fossilFileNameOnly
    variable fossilInfoCommand
    variable fossilInfoProjectCodePattern
    variable projectCode
    variable scriptDirectory

    fossilMustBeInstalled


  #
  # NOTE: This procedure attempts to verify that the checkout directory does
  #       belong to the correct branch.  There are no arguments.  Non-zero
  #       is returned if the verification is successful.
  #
  proc verifyThisIsTheCorrectBranch {} {
    variable fossilFileNameOnly
    variable fossilInfoCommand
    variable fossilInfoTagsPattern
    variable scriptDirectory

    fossilMustBeInstalled

    if {[isEagle]} then {

  #
  # NOTE: This procedure attempts to change the branch for the checkout
  #       directory.  There are no arguments.  This procedure may raise
  #       script errors.
  #
  proc changeToTheCorrectBranch {} {
    variable checkoutDirectory
    variable fossilFileNameOnly
    variable fossilUpdateCommand

    fossilMustBeInstalled
    verifyCheckoutDirectory

    if {[isEagle]} then {
      set directory [::PackageRepository::formatExecArgument \

  #       Fossil.  The targetDirectory argument is the fully qualified path
  #       to the package platform directory.  The fileName argument is the
  #       relative name of the file to be staged.  This procedure may raise
  #       script errors.
  #
  proc stageOnePackageFile { targetDirectory fileName } {
    variable fossilAddCommand
    variable fossilFileNameOnly

    fossilMustBeInstalled

    if {[isEagle]} then {
      set directory [::PackageRepository::formatExecArgument \
          $targetDirectory]

  # NOTE: This procedure attempts to stage the specified package files using
  #       Fossil.  The fileNames argument is a list of (fully?) qualified
  #       local file names to stage.
  #
  proc stagePackageFiles { language version platform fileNames } {
    variable checkoutDirectory
    variable fossilAddCommand
    variable fossilFileNameOnly

    ::PackageDownloader::verifyLanguageAndVersion $language $version isClient

    if {$isClient} then {
      error "cannot stage files: client files must be committed directly"
    }

  #       is the name of a scalar variable in the context of the immediate
  #       caller that will receive the resulting Fossil check-in identifier.
  #
  proc commitPackageFiles { package patchLevel language version varName } {
    variable checkoutDirectory
    variable fossilCommitCommand
    variable fossilCommitPattern
    variable fossilFileNameOnly

    fossilMustBeInstalled
    verifyCheckoutDirectory

    set branch [appendArgs pkg_ $package _ $patchLevel]

    set comment [appendArgs \